diff --git a/sample-videochat-kotlin/app/build.gradle b/sample-videochat-kotlin/app/build.gradle
index 6d6d3bdf8..3d08a2c63 100644
--- a/sample-videochat-kotlin/app/build.gradle
+++ b/sample-videochat-kotlin/app/build.gradle
@@ -1,19 +1,16 @@
 buildscript {
     repositories {
         google()
-        jcenter()
-        maven { url 'https://maven.fabric.io/public' }
+        mavenCentral()
     }
     dependencies {
         classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlinGradlePluginVersion"
-        classpath "io.fabric.tools:gradle:$fabricToolsVersion"
     }
 }
 
 apply plugin: 'com.android.application'
 apply plugin: 'kotlin-android'
 apply plugin: 'kotlin-android-extensions'
-apply plugin: 'io.fabric'
 
 androidExtensions {
     experimental = true
@@ -21,27 +18,25 @@ androidExtensions {
 
 repositories {
     google()
-    jcenter()
+    mavenCentral()
     maven {
         url "https://github.com/QuickBlox/quickblox-android-sdk-releases/raw/master/"
     }
-    maven { url 'https://maven.fabric.io/public' }
-    flatDir { dirs 'libs' }
 }
 
 android {
-    def versionQACode = 3
+    def versionQACode = 1
 
-    compileSdkVersion 28
-    buildToolsVersion "28.0.3"
+    compileSdkVersion 31
+    buildToolsVersion "31.0.0"
     flavorDimensions dimensionDefault
 
     defaultConfig {
         applicationId "com.quickblox.sample.videochat.kotlin"
-        minSdkVersion 16
-        targetSdkVersion 28
-        versionCode 404000
-        versionName '4.0.4'
+        minSdkVersion 21
+        targetSdkVersion 31
+        versionCode 405000
+        versionName '4.0.5'
         multiDexEnabled true
     }
 
@@ -65,12 +60,14 @@ android {
             minifyEnabled false
             shrinkResources false
             proguardFile 'proguard-rules.pro'
-            zipAlignEnabled false
             resValue "string", "versionName", "QuickBlox Video Chat Kotlin\nBuild version " + defaultConfig.getVersionName()
         }
 
         release {
             signingConfig signingConfigs.debug
+            minifyEnabled true
+            shrinkResources true
+            proguardFile 'proguard-rules.pro'
             resValue "string", "versionName", "QuickBlox Video Chat Kotlin\nBuild version " + defaultConfig.getVersionName()
         }
     }
@@ -95,21 +92,14 @@ android {
 }
 
 dependencies {
-
     implementation "com.quickblox:quickblox-android-sdk-videochat-webrtc:$qbSdkVersion"
     implementation "com.quickblox:quickblox-android-sdk-messages:$qbSdkVersion"
-
     implementation "com.google.firebase:firebase-core:$firebaseCoreVersion"
-    implementation "com.github.bumptech.glide:glide:$glideVersion"
     implementation "com.google.android.material:material:$materialVersion"
     implementation "com.github.johnkil.android-robototextview:robototextview:$robotoTextViewVersion"
-    implementation "androidx.fragment:fragment:$fragmentAndroidXVersion"
-    implementation "androidx.lifecycle:lifecycle-viewmodel:$lifecycleViewmodelAndroidXVersion"
+    implementation "androidx.fragment:fragment-ktx:$fragmentAndroidXVersion"
+    implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:$lifecycleViewmodelAndroidXVersion"
     implementation "androidx.core:core-ktx:$coreKtxVersion"
-    implementation("com.crashlytics.sdk.android:crashlytics:$crashlyticsVersion@aar") {
-        transitive = true
-    }
-    compile "org.jetbrains.kotlin:kotlin-reflect:$kotlinReflectVersion"
 }
 
 apply from: "../artifacts.gradle"
diff --git a/sample-videochat-kotlin/app/google-services.json b/sample-videochat-kotlin/app/google-services.json
index 542e3ac38..97ec23e8e 100644
--- a/sample-videochat-kotlin/app/google-services.json
+++ b/sample-videochat-kotlin/app/google-services.json
@@ -1,154 +1,29 @@
 {
   "project_info": {
-    "project_number": "247738611464",
-    "firebase_url": "https://qb-prod-samples.firebaseio.com",
-    "project_id": "qb-prod-samples",
-    "storage_bucket": "qb-prod-samples.appspot.com"
+    "project_number": "Put here your value",
+    "firebase_url": "https://qb-samples.firebaseio.com",
+    "project_id": "qb-samples",
+    "storage_bucket": "qb-samples.appspot.com"
   },
   "client": [
     {
       "client_info": {
-        "mobilesdk_app_id": "1:247738611464:android:beb270faa2c3a789",
+        "mobilesdk_app_id": "Put here your value",
         "android_client_info": {
-          "package_name": "com.quickblox.sample.chat.java"
-        }
-      },
-      "oauth_client": [],
-      "api_key": [
-        {
-          "current_key": "AIzaSyBFXAfVr6kkFJdDNOm8U-c7iju0qIUkc_A"
-        }
-      ],
-      "services": {
-        "appinvite_service": {
-          "other_platform_oauth_client": [
-            {
-              "client_id": "247738611464-v2nvd29bmqum7niosnfuh28oq3beh9f6.apps.googleusercontent.com",
-              "client_type": 3
-            }
-          ]
-        }
-      }
-    },
-    {
-      "client_info": {
-        "mobilesdk_app_id": "1:247738611464:android:1cdc72e9ffd29448",
-        "android_client_info": {
-          "package_name": "com.quickblox.sample.chat.kotlin"
-        }
-      },
-      "oauth_client": [],
-      "api_key": [
-        {
-          "current_key": "AIzaSyBFXAfVr6kkFJdDNOm8U-c7iju0qIUkc_A"
-        }
-      ],
-      "services": {
-        "appinvite_service": {
-          "other_platform_oauth_client": [
-            {
-              "client_id": "247738611464-v2nvd29bmqum7niosnfuh28oq3beh9f6.apps.googleusercontent.com",
-              "client_type": 3
-            }
-          ]
-        }
-      }
-    },
-    {
-      "client_info": {
-        "mobilesdk_app_id": "1:247738611464:android:06cb0de4c719ad84",
-        "android_client_info": {
-          "package_name": "com.quickblox.sample.pushnotifications.java"
-        }
-      },
-      "oauth_client": [],
-      "api_key": [
-        {
-          "current_key": "AIzaSyBFXAfVr6kkFJdDNOm8U-c7iju0qIUkc_A"
-        }
-      ],
-      "services": {
-        "appinvite_service": {
-          "other_platform_oauth_client": [
-            {
-              "client_id": "247738611464-v2nvd29bmqum7niosnfuh28oq3beh9f6.apps.googleusercontent.com",
-              "client_type": 3
-            }
-          ]
-        }
-      }
-    },
-    {
-      "client_info": {
-        "mobilesdk_app_id": "1:247738611464:android:c2749661061637f0",
-        "android_client_info": {
-          "package_name": "com.quickblox.sample.pushnotifications.kotlin"
-        }
-      },
-      "oauth_client": [],
-      "api_key": [
-        {
-          "current_key": "AIzaSyBFXAfVr6kkFJdDNOm8U-c7iju0qIUkc_A"
-        }
-      ],
-      "services": {
-        "appinvite_service": {
-          "other_platform_oauth_client": [
-            {
-              "client_id": "247738611464-v2nvd29bmqum7niosnfuh28oq3beh9f6.apps.googleusercontent.com",
-              "client_type": 3
-            }
-          ]
-        }
-      }
-    },
-    {
-      "client_info": {
-        "mobilesdk_app_id": "1:247738611464:android:99e5b55a490c901c",
-        "android_client_info": {
-          "package_name": "com.quickblox.sample.videochat.java"
+          "package_name": "com.quickblox.sample.videochat.kotlin"
         }
       },
-      "oauth_client": [],
-      "api_key": [
+      "oauth_client": [
         {
-          "current_key": "AIzaSyBFXAfVr6kkFJdDNOm8U-c7iju0qIUkc_A"
+          "client_id": "Put here your value",
+          "client_type": 3
         }
       ],
-      "services": {
-        "appinvite_service": {
-          "other_platform_oauth_client": [
-            {
-              "client_id": "247738611464-v2nvd29bmqum7niosnfuh28oq3beh9f6.apps.googleusercontent.com",
-              "client_type": 3
-            }
-          ]
-        }
-      }
-    },
-    {
-      "client_info": {
-        "mobilesdk_app_id": "1:247738611464:android:ac22e0d1b3a3e86b",
-        "android_client_info": {
-          "package_name": "com.quickblox.sample.videochat.kotlin"
-        }
-      },
-      "oauth_client": [],
       "api_key": [
         {
-          "current_key": "AIzaSyBFXAfVr6kkFJdDNOm8U-c7iju0qIUkc_A"
-        }
-      ],
-      "services": {
-        "appinvite_service": {
-          "other_platform_oauth_client": [
-            {
-              "client_id": "247738611464-v2nvd29bmqum7niosnfuh28oq3beh9f6.apps.googleusercontent.com",
-              "client_type": 3
-            }
-          ]
+          "current_key": "Put here your value"
         }
-      }
+      ]
     }
   ],
   "configuration_version": "1"
diff --git a/sample-videochat-kotlin/app/proguard-rules.pro b/sample-videochat-kotlin/app/proguard-rules.pro
index f1b424510..7c835c9ff 100644
--- a/sample-videochat-kotlin/app/proguard-rules.pro
+++ b/sample-videochat-kotlin/app/proguard-rules.pro
@@ -1,6 +1,8 @@
 # Add project specific ProGuard rules here.
-# You can control the set of applied configuration files using the
-# proguardFiles setting in build.gradle.
+# By default, the flags in this file are appended to flags specified
+# in /home/tereha/Android/sdk/tools/proguard/proguard-android.txt
+# You can edit the include path and order by changing the proguardFiles
+# directive in build.gradle.
 #
 # For more details, see
 #   http://developer.android.com/guide/developing/tools/proguard.html
@@ -11,11 +13,32 @@
 #-keepclassmembers class fqcn.of.javascript.interface.for.webview {
 #   public *;
 #}
+#-dontusemixedcaseclassnames
+#-dontskipnonpubliclibraryclasses
+#-verbose
+#
+
+##---------------Begin: proguard configuration for Gson  ----------
+# Gson uses generic type information stored in a class file when working with fields. Proguard
+# removes such information by default, so configure it to keep all of it.
+-keepattributes EnclosingMethod
+-keepattributes InnerClasses
+-keepattributes Signature
+-keepattributes Exceptions
+
+# For using GSON @Expose annotation
+-keepattributes *Annotation*
+
+#quickblox sdk
+-keep class com.quickblox.** { *; }
+
+#smack xmpp library
+-keep class org.jxmpp.** { *; }
+-keep class org.jivesoftware.** { *; }
+-dontwarn org.jivesoftware.**
 
-# Uncomment this to preserve the line number information for
-# debugging stack traces.
-#-keepattributes SourceFile,LineNumberTable
+#webrtc
+-keep class org.webrtc.** { *; }
 
-# If you keep the line number information, uncomment this to
-# hide the original source file name.
-#-renamesourcefileattribute SourceFile
+#google gms
+-keep class com.google.android.gms.** { *; }
\ No newline at end of file
diff --git a/sample-videochat-kotlin/app/src/main/AndroidManifest.xml b/sample-videochat-kotlin/app/src/main/AndroidManifest.xml
index b271a0c97..1f9e4169f 100644
--- a/sample-videochat-kotlin/app/src/main/AndroidManifest.xml
+++ b/sample-videochat-kotlin/app/src/main/AndroidManifest.xml
@@ -3,7 +3,6 @@
     xmlns:tools="http://schemas.android.com/tools"
     package="com.quickblox.sample.videochat.kotlin">
 
-    <uses-permission android:name="android.permission.BLUETOOTH" />
     <uses-permission android:name="android.permission.CAMERA" />
     <uses-permission android:name="android.permission.MODIFY_AUDIO_SETTINGS" />
     <uses-permission android:name="android.permission.RECORD_AUDIO" />
@@ -12,7 +11,7 @@
     <uses-permission android:name="com.quickblox.sample.messages.permission.C2D_MESSAGE" />
     <uses-permission android:name="com.google.android.c2dm.permission.RECEIVE" />
     <uses-permission android:name="android.permission.FOREGROUND_SERVICE" />
-    <uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW"/>
+    <uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />
     <uses-permission android:name="android.permission.ACTION_MANAGE_OVERLAY_PERMISSION" />
 
     <application
@@ -26,6 +25,7 @@
 
         <activity
             android:name=".activities.SplashActivity"
+            android:exported="true"
             android:screenOrientation="portrait">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />
@@ -64,15 +64,21 @@
 
         <service android:name=".services.LoginService" />
 
-        <service android:name=".services.CallService" />
+        <service
+            android:foregroundServiceType="mediaProjection"
+            android:name=".services.CallService" />
 
-        <service android:name=".services.fcm.PushListenerService">
+        <service
+            android:name=".services.fcm.PushListenerService"
+            android:exported="false">
             <intent-filter>
                 <action android:name="com.google.firebase.MESSAGING_EVENT" />
             </intent-filter>
         </service>
 
-        <service android:name="com.quickblox.messages.services.fcm.QBFcmPushInstanceIDService">
+        <service
+            android:name="com.quickblox.messages.services.fcm.QBFcmPushInstanceIDService"
+            android:exported="false">
             <intent-filter>
                 <action android:name="com.google.firebase.INSTANCE_ID_EVENT" />
             </intent-filter>
diff --git a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/App.kt b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/App.kt
index 3de0ac38d..81bd0a966 100644
--- a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/App.kt
+++ b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/App.kt
@@ -1,10 +1,8 @@
 package com.quickblox.sample.videochat.kotlin
 
 import android.app.Application
-import com.crashlytics.android.Crashlytics
 import com.quickblox.auth.session.QBSettings
 import com.quickblox.sample.videochat.kotlin.db.DbHelper
-import io.fabric.sdk.android.Fabric
 
 //User default credentials
 const val DEFAULT_USER_PASSWORD = "quickblox"
@@ -30,17 +28,10 @@ class App : Application() {
         super.onCreate()
         instance = this
         dbHelper = DbHelper(this)
-        initFabric()
         checkCredentials()
         initCredentials()
     }
 
-    private fun initFabric() {
-        if (!BuildConfig.DEBUG) {
-            Fabric.with(this, Crashlytics())
-        }
-    }
-
     private fun checkCredentials() {
         if (APPLICATION_ID.isEmpty() || AUTH_KEY.isEmpty() || AUTH_SECRET.isEmpty() || ACCOUNT_KEY.isEmpty()) {
             throw AssertionError(getString(R.string.error_qb_credentials_empty))
diff --git a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/activities/AppInfoActivity.kt b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/activities/AppInfoActivity.kt
index 98f403eef..626995549 100644
--- a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/activities/AppInfoActivity.kt
+++ b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/activities/AppInfoActivity.kt
@@ -75,8 +75,8 @@ class AppInfoActivity : AppCompatActivity() {
         }
     }
 
-    override fun onOptionsItemSelected(item: MenuItem?): Boolean {
-        when (item?.itemId) {
+    override fun onOptionsItemSelected(item: MenuItem): Boolean {
+        when (item.itemId) {
             android.R.id.home -> {
                 finish()
                 return true
diff --git a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/activities/BaseActivity.kt b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/activities/BaseActivity.kt
index e3f42bc5d..a6a88b1a3 100644
--- a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/activities/BaseActivity.kt
+++ b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/activities/BaseActivity.kt
@@ -36,7 +36,7 @@ abstract class BaseActivity : AppCompatActivity() {
     }
 
     internal fun hideProgressDialog() {
-        if (progressDialog != null && progressDialog!!.isShowing) {
+        if (progressDialog != null && progressDialog?.isShowing == true) {
             progressDialog!!.dismiss()
         }
     }
diff --git a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/activities/CallActivity.kt b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/activities/CallActivity.kt
index 292f66abf..54197eaae 100644
--- a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/activities/CallActivity.kt
+++ b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/activities/CallActivity.kt
@@ -19,6 +19,7 @@ import com.quickblox.sample.videochat.kotlin.db.QbUsersDbManager
 import com.quickblox.sample.videochat.kotlin.fragments.*
 import com.quickblox.sample.videochat.kotlin.services.CallService
 import com.quickblox.sample.videochat.kotlin.services.LoginService
+import com.quickblox.sample.videochat.kotlin.services.ONE_OPPONENT
 import com.quickblox.sample.videochat.kotlin.util.loadUsersByIds
 import com.quickblox.sample.videochat.kotlin.utils.*
 import com.quickblox.users.model.QBUser
@@ -31,7 +32,7 @@ import com.quickblox.videochat.webrtc.view.QBRTCVideoTrack
 import org.jivesoftware.smack.AbstractConnectionListener
 import org.jivesoftware.smack.ConnectionListener
 import org.webrtc.CameraVideoCapturer
-import java.util.HashMap
+import java.util.*
 import kotlin.collections.ArrayList
 
 private const val INCOME_CALL_FRAGMENT = "income_call_fragment"
@@ -265,17 +266,9 @@ class CallActivity : BaseActivity(), IncomeCallFragmentCallbackListener, QBRTCSe
     }
 
     private fun initIncomingCallTask() {
-        showIncomingCallWindowTaskHandler = Handler(Looper.myLooper())
+        showIncomingCallWindowTaskHandler = Handler(Looper.getMainLooper())
         showIncomingCallWindowTask = Runnable {
             if (callService.currentSessionExist()) {
-                /*val currentSessionState = callService.getCurrentSessionState()
-                if (BaseSession.QBRTCSessionState.QB_RTC_SESSION_NEW == currentSessionState) {
-                    callService.rejectCurrentSession(HashMap())
-                } else {
-                    callService.stopRingtone()
-                    hangUpCurrentSession()
-                }*/
-                // This is a fix to prevent call stop in case calling to user with more then one device logged in.
                 longToast("Call was stopped by UserNoActions timer")
                 callService.clearCallState()
                 callService.clearButtonsState()
@@ -316,14 +309,14 @@ class CallActivity : BaseActivity(), IncomeCallFragmentCallbackListener, QBRTCSe
     }
 
     override fun finish() {
-        //Fix bug when user returns to call from service and the backstack doesn't have any screens
+        // fix bug when user returns to call from service and the backstack doesn't have any screens
         OpponentsActivity.start(this)
         CallService.stop(this)
         super.finish()
     }
 
     override fun onBackPressed() {
-        // To prevent returning from Call Fragment
+        // to prevent returning from Call Fragment
     }
 
     private fun addIncomeCallFragment() {
@@ -366,8 +359,6 @@ class CallActivity : BaseActivity(), IncomeCallFragmentCallbackListener, QBRTCSe
         }
     }
 
-    ////////////////////////////// ConnectionListener //////////////////////////////
-
     private inner class ConnectionListenerImpl : AbstractConnectionListener() {
         override fun connectionClosedOnError(e: Exception?) {
             showNotificationPopUp(R.string.connection_was_lost, true)
@@ -378,10 +369,8 @@ class CallActivity : BaseActivity(), IncomeCallFragmentCallbackListener, QBRTCSe
         }
     }
 
-    ////////////////////////////// QBRTCSessionStateCallbackListener ///////////////////////////
-
     override fun onDisconnectedFromUser(session: QBRTCSession?, userId: Int?) {
-
+        // empty
     }
 
     override fun onConnectedToUser(session: QBRTCSession?, userId: Int?) {
@@ -393,15 +382,13 @@ class CallActivity : BaseActivity(), IncomeCallFragmentCallbackListener, QBRTCSe
     }
 
     override fun onConnectionClosedForUser(session: QBRTCSession?, userId: Int?) {
-
+        // empty
     }
 
     override fun onStateChanged(session: QBRTCSession?, sessiontState: BaseSession.QBRTCSessionState?) {
-
+        // empty
     }
 
-    ////////////////////////////// QBRTCClientSessionCallbacks //////////////////////////////
-
     override fun onUserNotAnswer(session: QBRTCSession?, userId: Int?) {
         if (callService.isCurrentSession(session)) {
             callService.stopRingtone()
@@ -417,9 +404,9 @@ class CallActivity : BaseActivity(), IncomeCallFragmentCallbackListener, QBRTCSe
 
     override fun onReceiveHangUpFromUser(session: QBRTCSession?, userId: Int?, map: MutableMap<String, String>?) {
         if (callService.isCurrentSession(session)) {
-            if (userId == session?.callerID) {
+            val numberOpponents = session?.opponents?.size
+            if (numberOpponents == ONE_OPPONENT) {
                 hangUpCurrentSession()
-                Log.d(TAG, "initiator hung up the call")
             }
             val participant = QbUsersDbManager.getUserById(userId)
             val participantName = if (participant != null) participant.fullName else userId.toString()
@@ -434,7 +421,7 @@ class CallActivity : BaseActivity(), IncomeCallFragmentCallbackListener, QBRTCSe
     }
 
     override fun onReceiveNewSession(session: QBRTCSession?) {
-
+        // empty
     }
 
     override fun onUserNoActions(session: QBRTCSession?, userId: Int?) {
@@ -454,8 +441,6 @@ class CallActivity : BaseActivity(), IncomeCallFragmentCallbackListener, QBRTCSe
         }
     }
 
-    ////////////////////////////// IncomeCallFragmentCallbackListener ////////////////////////////
-
     override fun onAcceptCurrentSession() {
         if (callService.currentSessionExist()) {
             addConversationFragment(true)
@@ -468,8 +453,6 @@ class CallActivity : BaseActivity(), IncomeCallFragmentCallbackListener, QBRTCSe
         callService.rejectCurrentSession(HashMap())
     }
 
-    ////////////////////////////// ConversationFragmentCallback ////////////////////////////
-
     override fun addConnectionListener(connectionCallback: ConnectionListener?) {
         callService.addConnectionListener(connectionCallback)
     }
@@ -533,9 +516,11 @@ class CallActivity : BaseActivity(), IncomeCallFragmentCallbackListener, QBRTCSe
     }
 
     override fun addOnChangeAudioDeviceListener(onChangeDynamicCallback: OnChangeAudioDevice?) {
+        // empty
     }
 
     override fun removeOnChangeAudioDeviceListener(onChangeDynamicCallback: OnChangeAudioDevice?) {
+        // empty
     }
 
     override fun acceptCall(userInfo: Map<String, String>) {
@@ -621,14 +606,14 @@ class CallActivity : BaseActivity(), IncomeCallFragmentCallbackListener, QBRTCSe
 
     private inner class CallServiceConnection : ServiceConnection {
         override fun onServiceDisconnected(name: ComponentName?) {
-
+            // empty
         }
 
         override fun onServiceConnected(name: ComponentName?, service: IBinder?) {
             val binder = service as CallService.CallServiceBinder
             callService = binder.getService()
             if (callService.currentSessionExist()) {
-                //we have already currentSession == null, so it's no reason to do further initialization
+                // we have already currentSession == null, so it's no reason to do further initialization
                 if (QBChatService.getInstance().isLoggedIn) {
                     initScreen()
                 } else {
diff --git a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/activities/LoginActivity.kt b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/activities/LoginActivity.kt
index ba59192f0..15f9d8a4b 100644
--- a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/activities/LoginActivity.kt
+++ b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/activities/LoginActivity.kt
@@ -29,7 +29,8 @@ class LoginActivity : BaseActivity() {
     private lateinit var user: QBUser
 
     companion object {
-        fun start(context: Context) = context.startActivity(Intent(context, LoginActivity::class.java))
+        fun start(context: Context) =
+            context.startActivity(Intent(context, LoginActivity::class.java))
     }
 
     override fun onCreate(savedInstanceState: Bundle?) {
@@ -125,7 +126,7 @@ class LoginActivity : BaseActivity() {
                 isLoginSuccess = it.getBooleanExtra(EXTRA_LOGIN_RESULT, false)
             }
 
-            var errorMessage = getString(R.string.unknown_error)
+            var errorMessage: String? = getString(R.string.unknown_error)
             data?.let {
                 errorMessage = it.getStringExtra(EXTRA_LOGIN_ERROR_MESSAGE)
             }
@@ -181,7 +182,8 @@ class LoginActivity : BaseActivity() {
         LoginService.start(this, qbUser, pendingIntent)
     }
 
-    private inner class LoginEditTextWatcher internal constructor(private val editText: EditText) : TextWatcher {
+    private inner class LoginEditTextWatcher internal constructor(private val editText: EditText) :
+        TextWatcher {
 
         override fun beforeTextChanged(s: CharSequence, start: Int, count: Int, after: Int) {
 
diff --git a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/activities/PermissionsActivity.kt b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/activities/PermissionsActivity.kt
index ebd46d0ae..3c9c5cdde 100644
--- a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/activities/PermissionsActivity.kt
+++ b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/activities/PermissionsActivity.kt
@@ -34,9 +34,6 @@ class PermissionsActivity : BaseActivity() {
 
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
-        if (intent == null || !intent.hasExtra(EXTRA_PERMISSIONS)) {
-            throw RuntimeException("This Activity needs to be launched using the static startActivityForResult() method.")
-        }
         setContentView(R.layout.activity_permissions)
         supportActionBar?.hide()
         requiresCheck = true
@@ -44,6 +41,10 @@ class PermissionsActivity : BaseActivity() {
 
     override fun onResume() {
         super.onResume()
+        if (intent == null || !intent.hasExtra(EXTRA_PERMISSIONS)) {
+            throw RuntimeException("This Activity needs to be launched using the static startActivityForResult() method.")
+        }
+
         if (requiresCheck) {
             checkPermissions()
         } else {
@@ -52,8 +53,9 @@ class PermissionsActivity : BaseActivity() {
     }
 
     private fun checkPermissions() {
-        val permissions = getPermissions()
-        val checkOnlyAudio = getCheckOnlyAudio()
+        val permissions = intent.getStringArrayExtra(EXTRA_PERMISSIONS)!!
+
+        val checkOnlyAudio = intent.getBooleanExtra(CHECK_ONLY_AUDIO, false)
 
         if (checkOnlyAudio) {
             checkPermissionAudio(permissions[1])
@@ -78,14 +80,6 @@ class PermissionsActivity : BaseActivity() {
         }
     }
 
-    private fun getPermissions(): Array<String> {
-        return intent.getStringArrayExtra(EXTRA_PERMISSIONS)
-    }
-
-    private fun getCheckOnlyAudio(): Boolean {
-        return intent.getBooleanExtra(CHECK_ONLY_AUDIO, false)
-    }
-
     private fun requestPermissions(vararg permissions: String) {
         ActivityCompat.requestPermissions(this, permissions, PERMISSION_CODE)
     }
@@ -96,6 +90,7 @@ class PermissionsActivity : BaseActivity() {
     }
 
     override fun onRequestPermissionsResult(requestCode: Int, permissions: Array<String>, grantResults: IntArray) {
+        super.onRequestPermissionsResult(requestCode, permissions, grantResults)
         if (requestCode == PERMISSION_CODE && hasAllPermissionsGranted(grantResults)) {
             requiresCheck = true
             allPermissionsGranted()
diff --git a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/fragments/BaseConversationFragment.kt b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/fragments/BaseConversationFragment.kt
index c3b398b5a..9707db697 100644
--- a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/fragments/BaseConversationFragment.kt
+++ b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/fragments/BaseConversationFragment.kt
@@ -1,6 +1,7 @@
 package com.quickblox.sample.videochat.kotlin.fragments
 
 import android.app.Activity
+import android.content.Context
 import android.os.Bundle
 import android.util.Log
 import android.view.LayoutInflater
@@ -50,8 +51,8 @@ abstract class BaseConversationFragment : BaseToolBarFragment(), CallActivity.Cu
         }
     }
 
-    override fun onAttach(activity: Activity?) {
-        super.onAttach(activity)
+    override fun onAttach(context: Context) {
+        super.onAttach(context)
         try {
             conversationFragmentCallback = context as ConversationFragmentCallback
         } catch (e: ClassCastException) {
@@ -191,7 +192,6 @@ abstract class BaseConversationFragment : BaseToolBarFragment(), CallActivity.Cu
     }
 
     override fun onCallStopped() {
-        CallService.stop(activity as Activity)
         isStarted = false
         clearButtonsState()
         actionButtonsEnabled(false)
diff --git a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/fragments/IncomeCallFragment.kt b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/fragments/IncomeCallFragment.kt
index 707f6ec36..e12090bc9 100644
--- a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/fragments/IncomeCallFragment.kt
+++ b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/fragments/IncomeCallFragment.kt
@@ -60,8 +60,8 @@ class IncomeCallFragment : Fragment(), Serializable, View.OnClickListener {
     private lateinit var incomeCallFragmentCallbackListener: IncomeCallFragmentCallbackListener
     private var currentSession: QBRTCSession? = null
 
-    override fun onAttach(activity: Activity?) {
-        super.onAttach(activity)
+    override fun onAttach(context: Context) {
+        super.onAttach(context)
         try {
             incomeCallFragmentCallbackListener = activity as IncomeCallFragmentCallbackListener
         } catch (e: ClassCastException) {
diff --git a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/fragments/PreviewFragment.kt b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/fragments/PreviewFragment.kt
index 14c31b893..66d56f8ff 100644
--- a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/fragments/PreviewFragment.kt
+++ b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/fragments/PreviewFragment.kt
@@ -6,10 +6,8 @@ import android.view.View
 import android.view.ViewGroup
 import android.widget.ImageView
 import androidx.fragment.app.Fragment
-import com.bumptech.glide.Glide
-import com.bumptech.glide.load.engine.DiskCacheStrategy
 import com.quickblox.sample.videochat.kotlin.R
-import com.quickblox.sample.videochat.kotlin.utils.getDimen
+import com.quickblox.sample.videochat.kotlin.utils.getDrawable
 
 private const val PREVIEW_IMAGE = "preview_image"
 
@@ -27,11 +25,13 @@ class PreviewFragment : Fragment() {
 
     override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
         val view = inflater.inflate(R.layout.fragment_item_screen_share, container, false)
-        Glide.with(activity)
-                .load(arguments?.getInt(PREVIEW_IMAGE))
-                .diskCacheStrategy(DiskCacheStrategy.ALL)
-                .override(getDimen(R.dimen.pager_image_width), getDimen(R.dimen.pager_image_height))
-                .into(view.findViewById(R.id.image_preview) as ImageView)
+
+        val ivPreview = view.findViewById<ImageView>(R.id.image_preview)
+        val imageDrawable = arguments?.getInt(PREVIEW_IMAGE)
+
+        imageDrawable?.let {
+            ivPreview.setImageDrawable(getDrawable(it))
+        }
         return view
     }
 }
\ No newline at end of file
diff --git a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/fragments/ScreenShareFragment.kt b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/fragments/ScreenShareFragment.kt
index b8788e955..dfa07de19 100644
--- a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/fragments/ScreenShareFragment.kt
+++ b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/fragments/ScreenShareFragment.kt
@@ -48,13 +48,13 @@ class ScreenShareFragment : BaseToolBarFragment() {
         (activity as CallActivity).addCurrentCallStateListener(currentCallStateCallback!!)
     }
 
-    override fun onCreateOptionsMenu(menu: Menu?, inflater: MenuInflater?) {
-        inflater?.inflate(R.menu.screen_share_fragment, menu)
+    override fun onCreateOptionsMenu(menu: Menu, inflater: MenuInflater) {
+        inflater.inflate(R.menu.screen_share_fragment, menu)
         super.onCreateOptionsMenu(menu, inflater)
     }
 
-    override fun onOptionsItemSelected(item: MenuItem?): Boolean {
-        when (item?.itemId) {
+    override fun onOptionsItemSelected(item: MenuItem): Boolean {
+        when (item.itemId) {
             R.id.stop_screen_share -> {
                 Log.d(TAG, "stop_screen_share")
                 onSharingEvents?.onStopPreview()
@@ -64,7 +64,7 @@ class ScreenShareFragment : BaseToolBarFragment() {
         }
     }
 
-    override fun onAttach(context: Context?) {
+    override fun onAttach(context: Context) {
         super.onAttach(context)
         try {
             onSharingEvents = context as OnSharingEvents?
diff --git a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/fragments/VideoConversationFragment.kt b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/fragments/VideoConversationFragment.kt
index b5747142a..f5514ac0b 100644
--- a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/fragments/VideoConversationFragment.kt
+++ b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/fragments/VideoConversationFragment.kt
@@ -1,6 +1,5 @@
 package com.quickblox.sample.videochat.kotlin.fragments
 
-import android.app.Activity
 import android.content.Context
 import android.graphics.Color
 import android.graphics.Rect
@@ -18,8 +17,9 @@ import androidx.core.content.ContextCompat
 import androidx.recyclerview.widget.LinearLayoutManager
 import androidx.recyclerview.widget.RecyclerView
 import com.quickblox.sample.videochat.kotlin.R
+import com.quickblox.sample.videochat.kotlin.activities.CallActivity
 import com.quickblox.sample.videochat.kotlin.adapters.OpponentsFromCallAdapter
-import com.quickblox.sample.videochat.kotlin.services.CallService
+import com.quickblox.sample.videochat.kotlin.db.QbUsersDbManager
 import com.quickblox.sample.videochat.kotlin.utils.SharedPrefsHelper
 import com.quickblox.sample.videochat.kotlin.utils.shortToast
 import com.quickblox.users.model.QBUser
@@ -50,13 +50,12 @@ class VideoConversationFragment : BaseConversationFragment(), Serializable,
     OpponentsFromCallAdapter.OnAdapterEventListener {
     private val TAG = VideoConversationFragment::class.java.simpleName
 
-    //Views
     private lateinit var cameraToggle: ToggleButton
     private var parentView: View? = null
     private lateinit var actionVideoButtonsLayout: LinearLayout
     private lateinit var connectionStatusLocal: TextView
     private lateinit var recyclerView: RecyclerView
-    private lateinit var localVideoView: QBRTCSurfaceView
+    private var localVideoView: QBRTCSurfaceView? = null
     private var remoteFullScreenVideoView: QBRTCSurfaceView? = null
 
     private lateinit var opponentViewHolders: SparseArray<OpponentsFromCallAdapter.ViewHolder>
@@ -74,90 +73,49 @@ class VideoConversationFragment : BaseConversationFragment(), Serializable,
     private var isCurrentCameraFront: Boolean = false
     private var isLocalVideoFullScreen: Boolean = false
 
-    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
-        parentView = super.onCreateView(inflater, container, savedInstanceState)
-        return parentView
-    }
-
-    override fun configureOutgoingScreen() {
-        val context = activity!!
-        outgoingOpponentsRelativeLayout.setBackgroundColor(ContextCompat.getColor(context, R.color.grey_transparent_50))
-        allOpponentsTextView.setTextColor(ContextCompat.getColor(context, R.color.white))
-        ringingTextView.setTextColor(ContextCompat.getColor(context, R.color.white))
-    }
-
-    override fun configureActionBar() {
-        actionBar.setDisplayShowTitleEnabled(false)
-    }
-
-    override fun configureToolbar() {
-        val context = activity!!
-        toolbar.visibility = View.VISIBLE
-        toolbar.setBackgroundColor(ContextCompat.getColor(context, R.color.black_transparent_50))
-        toolbar.setTitleTextColor(ContextCompat.getColor(context, R.color.white))
-        toolbar.setSubtitleTextColor(ContextCompat.getColor(context, R.color.white))
-    }
-
     override fun getFragmentLayout(): Int {
         return R.layout.fragment_video_conversation
     }
 
-    override fun initFields() {
-        super.initFields()
-        localViewOnClickListener = LocalViewOnClickListener()
-        amountOpponents = opponents.size
-        allOpponents = Collections.synchronizedList(ArrayList(opponents.size))
-        allOpponents.addAll(opponents)
-
-        timerCallText = activity!!.findViewById(R.id.timer_call)
-
-        isPeerToPeerCall = opponents.size == 1
-    }
-
-    private fun setDuringCallActionBar() {
-        actionBar.setDisplayShowTitleEnabled(true)
-        actionBar.title = currentUser.fullName
-        if (isPeerToPeerCall) {
-            actionBar.subtitle = getString(R.string.opponent, opponents[0].fullName)
-        } else {
-            actionBar.subtitle = getString(R.string.opponents, amountOpponents.toString())
-        }
-
-        actionButtonsEnabled(true)
-    }
-
-    private fun addListeners() {
-        conversationFragmentCallback?.addSessionStateListener(this)
-        conversationFragmentCallback?.addSessionEventsListener(this)
-        conversationFragmentCallback?.addVideoTrackListener(this)
-    }
-
-    private fun removeListeners() {
-        conversationFragmentCallback?.removeSessionStateListener(this)
-        conversationFragmentCallback?.removeSessionEventsListener(this)
-        conversationFragmentCallback?.removeVideoTrackListener(this)
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        setHasOptionsMenu(true)
     }
 
-    override fun actionButtonsEnabled(inability: Boolean) {
-        super.actionButtonsEnabled(inability)
-        cameraToggle.isEnabled = inability
-        // inactivate toggle buttons
-        cameraToggle.isActivated = inability
+    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
+        parentView = super.onCreateView(inflater, container, savedInstanceState)
+        return parentView
     }
 
     override fun onStart() {
         super.onStart()
-        Log.i(TAG, "onStart")
         if (!allCallbacksInit) {
             addListeners()
             allCallbacksInit = true
         }
     }
 
-    override fun onCreate(savedInstanceState: Bundle?) {
-        super.onCreate(savedInstanceState)
-        Log.i(TAG, "onCreate")
-        setHasOptionsMenu(true)
+    override fun onResume() {
+        super.onResume()
+        toggleCamera(cameraToggle.isChecked)
+    }
+
+    override fun onPause() {
+        // if camera state is CameraState.ENABLED_FROM_USER or CameraState.NONE
+        // than we turn off cam
+        toggleCamera(false)
+
+        if (connectionEstablished) {
+            allCallbacksInit = false
+        } else {
+            Log.d(TAG, "We are in dialing process yet!")
+        }
+
+        releaseViewHolders()
+        removeListeners()
+        releaseViews()
+
+        super.onPause()
     }
 
     override fun initViews(view: View?) {
@@ -171,7 +129,7 @@ class VideoConversationFragment : BaseConversationFragment(), Serializable,
         isCurrentCameraFront = true
         localVideoView = view.findViewById(R.id.local_video_view)
         initCorrectSizeForLocalView()
-        localVideoView.setZOrderMediaOverlay(true)
+        localVideoView?.setZOrderMediaOverlay(true)
 
         remoteFullScreenVideoView = view.findViewById(R.id.remote_video_view)
         remoteFullScreenVideoView?.setOnClickListener(localViewOnClickListener)
@@ -183,10 +141,10 @@ class VideoConversationFragment : BaseConversationFragment(), Serializable,
             recyclerView.addItemDecoration(DividerItemDecoration(context, R.dimen.grid_item_divider))
             recyclerView.setHasFixedSize(true)
             val columnsCount = defineColumnsCount()
-            val layoutManager = LinearLayoutManager(activity, LinearLayout.HORIZONTAL, false)
+            val layoutManager = LinearLayoutManager(activity, RecyclerView.HORIZONTAL, false)
             recyclerView.layoutManager = layoutManager
 
-            //for correct removing item in adapter
+            // for correct removing item in adapter
             recyclerView.itemAnimator = null
             recyclerView.viewTreeObserver.addOnGlobalLayoutListener(object : ViewTreeObserver.OnGlobalLayoutListener {
                 override fun onGlobalLayout() {
@@ -212,6 +170,68 @@ class VideoConversationFragment : BaseConversationFragment(), Serializable,
         restoreSession()
     }
 
+    override fun initFields() {
+        super.initFields()
+        localViewOnClickListener = LocalViewOnClickListener()
+        amountOpponents = opponents.size
+        allOpponents = Collections.synchronizedList(ArrayList(opponents.size))
+        allOpponents.addAll(opponents)
+
+        timerCallText = activity!!.findViewById(R.id.timer_call)
+
+        isPeerToPeerCall = opponents.size == 1
+    }
+
+    override fun configureOutgoingScreen() {
+        val context = activity!!
+        outgoingOpponentsRelativeLayout.setBackgroundColor(ContextCompat.getColor(context, R.color.grey_transparent_50))
+        allOpponentsTextView.setTextColor(ContextCompat.getColor(context, R.color.white))
+        ringingTextView.setTextColor(ContextCompat.getColor(context, R.color.white))
+    }
+
+    override fun configureActionBar() {
+        actionBar.setDisplayShowTitleEnabled(false)
+    }
+
+    override fun configureToolbar() {
+        val context = activity!!
+        toolbar.visibility = View.VISIBLE
+        toolbar.setBackgroundColor(ContextCompat.getColor(context, R.color.black_transparent_50))
+        toolbar.setTitleTextColor(ContextCompat.getColor(context, R.color.white))
+        toolbar.setSubtitleTextColor(ContextCompat.getColor(context, R.color.white))
+    }
+
+    private fun setDuringCallActionBar() {
+        actionBar.setDisplayShowTitleEnabled(true)
+        actionBar.title = currentUser.fullName
+        if (isPeerToPeerCall) {
+            actionBar.subtitle = getString(R.string.opponent, opponents[0].fullName)
+        } else {
+            actionBar.subtitle = getString(R.string.opponents, amountOpponents.toString())
+        }
+
+        actionButtonsEnabled(true)
+    }
+
+    private fun addListeners() {
+        conversationFragmentCallback?.addSessionStateListener(this)
+        conversationFragmentCallback?.addSessionEventsListener(this)
+        conversationFragmentCallback?.addVideoTrackListener(this)
+    }
+
+    private fun removeListeners() {
+        conversationFragmentCallback?.removeSessionStateListener(this)
+        conversationFragmentCallback?.removeSessionEventsListener(this)
+        conversationFragmentCallback?.removeVideoTrackListener(this)
+    }
+
+    override fun actionButtonsEnabled(inability: Boolean) {
+        super.actionButtonsEnabled(inability)
+        cameraToggle.isEnabled = inability
+        // inactivate toggle buttons
+        cameraToggle.isActivated = inability
+    }
+
     private fun restoreSession() {
         Log.d(TAG, "restoreSession ")
         if (conversationFragmentCallback?.isCallState() == false) {
@@ -246,7 +266,7 @@ class VideoConversationFragment : BaseConversationFragment(), Serializable,
     }
 
     private fun initCorrectSizeForLocalView() {
-        val params = localVideoView.layoutParams
+        val params = localVideoView?.layoutParams
         val displaymetrics = resources.displayMetrics
 
         val screenWidthPx = displaymetrics.widthPixels
@@ -256,7 +276,7 @@ class VideoConversationFragment : BaseConversationFragment(), Serializable,
         val height = width / 2 * 3
         params?.width = width
         params?.height = height
-        localVideoView.layoutParams = params
+        localVideoView?.layoutParams = params
     }
 
     private fun setGrid(columnsCount: Int) {
@@ -282,42 +302,19 @@ class VideoConversationFragment : BaseConversationFragment(), Serializable,
         return opponents.size - 1
     }
 
-    override fun onResume() {
-        super.onResume()
-        Log.d(TAG, "onResume")
-        toggleCamera(cameraToggle.isChecked)
-    }
-
-    override fun onPause() {
-        // If camera state is CameraState.ENABLED_FROM_USER or CameraState.NONE
-        // than we turn off cam
-        toggleCamera(false)
-
-        if (connectionEstablished) {
-            allCallbacksInit = false
-        } else {
-            Log.d(TAG, "We are in dialing process yet!")
-        }
-
-        releaseViewHolders()
-        removeListeners()
-        releaseViews()
-
-        super.onPause()
-    }
-
-    override fun onDetach() {
-        super.onDetach()
-        Log.d(TAG, "onDetach")
-    }
-
     private fun releaseViewHolders() {
         opponentViewHolders.clear()
     }
 
     private fun releaseViews() {
-        localVideoView.release()
+        if (conversationFragmentCallback?.getCurrentSessionState() != BaseSession.QBRTCSessionState.QB_RTC_SESSION_CLOSED) {
+            for (item in (activity as CallActivity).getVideoTrackMap()) {
+                val renderer = item.value.renderer
+                item.value.removeRenderer(renderer)
+            }
+        }
 
+        localVideoView?.release()
         remoteFullScreenVideoView?.release()
 
         remoteFullScreenVideoView = null
@@ -328,7 +325,6 @@ class VideoConversationFragment : BaseConversationFragment(), Serializable,
 
     override fun onCallStopped() {
         super.onCallStopped()
-        CallService.stop(activity as Activity)
         Log.i(TAG, "onCallStopped")
     }
 
@@ -397,7 +393,6 @@ class VideoConversationFragment : BaseConversationFragment(), Serializable,
         }
     }
 
-    ////////////////////////////  callbacks from QBRTCClientVideoTracksCallbacks ///////////////////
     override fun onLocalVideoTrackReceive(qbrtcSession: QBRTCSession?, videoTrack: QBRTCVideoTrack) {
         Log.d(TAG, "onLocalVideoTrackReceive() run")
         localVideoTrack = videoTrack
@@ -424,12 +419,9 @@ class VideoConversationFragment : BaseConversationFragment(), Serializable,
             }
         }
     }
-    /////////////////////////////////////////    end    ////////////////////////////////////////////
 
-    //last opponent parentView is bind
     override fun onBindLastViewHolder(holder: OpponentsFromCallAdapter.ViewHolder, position: Int) {
         Log.i(TAG, "onBindLastViewHolder position=$position")
-
     }
 
     override fun onItemClick(position: Int) {
@@ -465,12 +457,12 @@ class VideoConversationFragment : BaseConversationFragment(), Serializable,
     }
 
     private fun swapUsersFullscreenToPreview(userId: Int) {
-        //      get opponentVideoTrack - opponent's video track from recyclerView
+        // get opponentVideoTrack - opponent's video track from recyclerView
         val videoTrackMap = conversationFragmentCallback?.getVideoTrackMap()
 
         val opponentVideoTrack = videoTrackMap?.get(userId)
 
-        //      get mainVideoTrack - opponent's video track from full screen
+        // get mainVideoTrack - opponent's video track from full screen
         val mainVideoTrack = videoTrackMap?.get(userIDFullScreen)
 
         val remoteVideoView = findHolder(userId)?.getOpponentView()
@@ -503,6 +495,7 @@ class VideoConversationFragment : BaseConversationFragment(), Serializable,
             fillVideoView(remoteVideoView, videoTrack, true)
         } else {
             isRemoteShown = true
+            itemHolder.getOpponentView().release()
             opponentsAdapter.removeItem(itemHolder.adapterPosition)
             setDuringCallActionBar()
             setRecyclerViewVisibleState()
@@ -562,7 +555,7 @@ class VideoConversationFragment : BaseConversationFragment(), Serializable,
     /**
      * @param userId set userId if it from fullscreen videoTrack
      */
-    private fun fillVideoView(videoView: QBRTCSurfaceView, videoTrack: QBRTCVideoTrack,
+    private fun fillVideoView(videoView: QBRTCSurfaceView?, videoTrack: QBRTCVideoTrack,
                               remoteRenderer: Boolean) {
         videoTrack.removeRenderer(videoTrack.renderer)
         videoTrack.addRenderer(videoView)
@@ -572,12 +565,12 @@ class VideoConversationFragment : BaseConversationFragment(), Serializable,
         Log.d(TAG, (if (remoteRenderer) "remote" else "local") + " Track is rendering")
     }
 
-    private fun updateVideoView(videoView: SurfaceViewRenderer, mirror: Boolean) {
+    private fun updateVideoView(videoView: SurfaceViewRenderer?, mirror: Boolean) {
         val scalingType = RendererCommon.ScalingType.SCALE_ASPECT_FILL
         Log.i(TAG, "updateVideoView mirror:$mirror, scalingType = $scalingType")
-        videoView.setScalingType(scalingType)
-        videoView.setMirror(mirror)
-        videoView.requestLayout()
+        videoView?.setScalingType(scalingType)
+        videoView?.setMirror(mirror)
+        videoView?.requestLayout()
     }
 
     /**
@@ -623,7 +616,6 @@ class VideoConversationFragment : BaseConversationFragment(), Serializable,
         val holder = getViewHolderForOpponent(userId) ?: return
 
         holder.getProgressBar().visibility = View.GONE
-
     }
 
     private fun setBackgroundOpponentView(userId: Int?) {
@@ -634,10 +626,8 @@ class VideoConversationFragment : BaseConversationFragment(), Serializable,
         }
     }
 
-    ///////////////////////////////  QBRTCSessionConnectionCallbacks ///////////////////////////
-
     override fun onStateChanged(qbrtcSession: QBRTCSession, qbrtcSessionState: BaseSession.QBRTCSessionState) {
-
+        // empty
     }
 
     override fun onConnectedToUser(qbrtcSession: QBRTCSession?, userId: Int) {
@@ -660,9 +650,6 @@ class VideoConversationFragment : BaseConversationFragment(), Serializable,
         setStatusForOpponent(integer, getString(R.string.text_status_disconnected))
     }
 
-    //////////////////////////////////   end     //////////////////////////////////////////
-
-    /////////////////// Callbacks from CallActivity.QBRTCSessionUserCallback //////////////////////
     override fun onUserNotAnswer(session: QBRTCSession, userId: Int) {
         setProgressBarForOpponentGone(userId)
         setStatusForOpponent(userId, getString(R.string.text_status_no_answer))
@@ -688,40 +675,41 @@ class VideoConversationFragment : BaseConversationFragment(), Serializable,
     }
 
     override fun onSessionClosed(session: QBRTCSession) {
-
+        // empty
     }
 
-    //////////////////////////////////   end     //////////////////////////////////////////
-
     private fun setAnotherUserToFullScreen() {
         if (opponentsAdapter.opponents.isEmpty()) {
             return
         }
-        val userId = opponentsAdapter.getItem(0)
-        // get opponentVideoTrack - opponent's video track from recyclerView
-        val opponentVideoTrack = conversationFragmentCallback?.getVideoTrack(userId) ?: return
+        for (user in opponents){
+            val videoTrack = conversationFragmentCallback?.getVideoTrack(user.id)
+            if (videoTrack != null){
+                val userFullScreen = QbUsersDbManager.getUserById(userIDFullScreen)
 
-        remoteFullScreenVideoView?.let {
-            fillVideoView(userId, it, opponentVideoTrack)
-            Log.d(TAG, "fullscreen enabled")
-        }
+                val itemHolder = findHolder(user.id)
+                itemHolder?.setUserId(userIDFullScreen)
+                itemHolder?.setUserName(userFullScreen?.fullName.toString())
+                itemHolder?.setStatus(getString(R.string.text_status_closed))
+                itemHolder?.getOpponentView()?.release()
 
-        val itemHolder = findHolder(userId)
-        if (itemHolder != null) {
-            opponentsAdapter.removeItem(itemHolder.adapterPosition)
-            itemHolder.getOpponentView().release()
-            Log.d(TAG, "onConnectionClosedForUser opponentsAdapter.removeItem= $userId")
+                remoteFullScreenVideoView?.let {
+                    fillVideoView(user.id, it, videoTrack)
+                    Log.d(TAG, "fullscreen enabled")
+                }
+                return
+            }
         }
     }
 
-    override fun onCreateOptionsMenu(menu: Menu?, inflater: MenuInflater?) {
-        inflater?.inflate(R.menu.conversation_fragment, menu)
+    override fun onCreateOptionsMenu(menu: Menu, inflater: MenuInflater) {
+        inflater.inflate(R.menu.conversation_fragment, menu)
         super.onCreateOptionsMenu(menu, inflater)
         optionsMenu = menu
     }
 
-    override fun onOptionsItemSelected(item: MenuItem?): Boolean {
-        when (item?.itemId) {
+    override fun onOptionsItemSelected(item: MenuItem): Boolean {
+        when (item.itemId) {
             R.id.camera_switch -> {
                 Log.d("Conversation", "camera_switch")
                 switchCamera(item)
@@ -762,7 +750,7 @@ class VideoConversationFragment : BaseConversationFragment(), Serializable,
     }
 
     private fun runUpdateUsersNames(newUsers: ArrayList<QBUser>) {
-        //need delayed for synchronization with recycler parentView initialization
+        // need delayed for synchronization with recycler parentView initialization
         mainHandler.postDelayed({
             for (user in newUsers) {
                 Log.d(TAG, "runUpdateUsersNames. foreach, user = " + user.fullName)
@@ -804,7 +792,7 @@ class VideoConversationFragment : BaseConversationFragment(), Serializable,
 
         private fun hideToolBarAndButtons() {
             actionBar.hide()
-            localVideoView.visibility = View.INVISIBLE
+            localVideoView?.visibility = View.INVISIBLE
             actionVideoButtonsLayout.visibility = View.GONE
             if (!isPeerToPeerCall) {
                 shiftBottomListOpponents()
@@ -813,7 +801,7 @@ class VideoConversationFragment : BaseConversationFragment(), Serializable,
 
         private fun showToolBarAndButtons() {
             actionBar.show()
-            localVideoView.visibility = View.VISIBLE
+            localVideoView?.visibility = View.VISIBLE
             actionVideoButtonsLayout.visibility = View.VISIBLE
             if (!isPeerToPeerCall) {
                 shiftMarginListOpponents()
diff --git a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/services/CallService.kt b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/services/CallService.kt
index d8bd27817..5c3595b69 100644
--- a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/services/CallService.kt
+++ b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/services/CallService.kt
@@ -36,17 +36,17 @@ import org.webrtc.CameraVideoCapturer
 import java.util.*
 import kotlin.collections.HashMap
 
-
 const val SERVICE_ID = 787
 const val CHANNEL_ID = "Quickblox channel"
 const val CHANNEL_NAME = "Quickblox background service"
+const val ONE_OPPONENT = 1
 
 class CallService : Service() {
     private var TAG = CallService::class.java.simpleName
 
     private val callServiceBinder: CallServiceBinder = CallServiceBinder()
 
-    private var videoTrackMap: MutableMap<Int, QBRTCVideoTrack> = java.util.HashMap()
+    private var videoTrackMap: MutableMap<Int, QBRTCVideoTrack> = HashMap()
     private lateinit var networkConnectionListener: NetworkConnectionListener
     private lateinit var networkConnectionChecker: NetworkConnectionChecker
     private lateinit var sessionEventsListener: SessionEventsListener
@@ -100,7 +100,6 @@ class CallService : Service() {
         super.onDestroy()
         networkConnectionChecker.unregisterListener(networkConnectionListener)
         removeConnectionListener(connectionListener)
-        removeVideoTrackRenders()
 
         releaseCurrentSession()
         releaseAudioManager()
@@ -113,17 +112,23 @@ class CallService : Service() {
         notificationManager.cancelAll()
     }
 
-    override fun onBind(intent: Intent?): IBinder? {
+    override fun onBind(intent: Intent?): IBinder {
         return callServiceBinder
     }
 
     private fun initNotification(): Notification {
+        var intentFlag = 0
+
         val notifyIntent = Intent(this, CallActivity::class.java).apply {
             flags = Intent.FLAG_ACTIVITY_NEW_TASK or Intent.FLAG_ACTIVITY_CLEAR_TASK
         }
 
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
+            intentFlag = PendingIntent.FLAG_IMMUTABLE
+        }
+
         val notifyPendingIntent = PendingIntent.getActivity(this, 0, notifyIntent,
-                PendingIntent.FLAG_UPDATE_CURRENT)
+            intentFlag)
 
         val notificationTitle = getString(R.string.notification_title)
         var notificationText = getString(R.string.notification_text, "")
@@ -232,7 +237,7 @@ class CallService : Service() {
         addSessionEventsListener(sessionEventsListener)
     }
 
-    fun initAudioManager() {
+    private fun initAudioManager() {
         appRTCAudioManager = AppRTCAudioManager.create(this)
 
         appRTCAudioManager.setOnWiredHeadsetStateListener { plugged, hasMicrophone ->
@@ -269,7 +274,6 @@ class CallService : Service() {
         currentSession = null
     }
 
-    //Listeners
     fun addConnectionListener(connectionListener: ConnectionListener?) {
         QBChatService.getInstance().addConnectionListener(connectionListener)
     }
@@ -294,11 +298,11 @@ class CallService : Service() {
         currentSession?.removeVideoTrackCallbacksListener(callback)
     }
 
-    fun addSignalingListener(callback: QBRTCSignalingCallback?) {
+    private fun addSignalingListener(callback: QBRTCSignalingCallback?) {
         currentSession?.addSignalingCallback(callback)
     }
 
-    fun removeSignalingListener(callback: QBRTCSignalingCallback?) {
+    private fun removeSignalingListener(callback: QBRTCSignalingCallback?) {
         currentSession?.removeSignalingCallback(callback)
     }
 
@@ -310,7 +314,6 @@ class CallService : Service() {
         rtcClient.removeSessionsCallbacksListener(callback)
     }
 
-    //Common methods
     fun acceptCall(userInfo: Map<String, String>) {
         currentSession?.acceptCall(userInfo)
     }
@@ -428,28 +431,12 @@ class CallService : Service() {
     }
 
     private fun removeVideoTrack(userId: Int) {
+        val videoTrack = getVideoTrack(userId)
+        val renderer =videoTrack?.renderer
+        videoTrack?.removeRenderer(renderer)
         videoTrackMap.remove(userId)
     }
 
-    private fun removeVideoTrackRenders() {
-        Log.d(TAG, "removeVideoTrackRenders")
-        if (videoTrackMap.isNotEmpty()) {
-            val entryIterator = videoTrackMap.entries.iterator()
-            while (entryIterator.hasNext()) {
-                val entry = entryIterator.next()
-                val userId = entry.key
-                val videoTrack = entry.value
-                val qbUser = QBChatService.getInstance().user
-                val remoteVideoTrack = userId != qbUser.id
-                if (remoteVideoTrack) {
-                    videoTrack.renderer?.let {
-                        videoTrack.removeRenderer(it)
-                    }
-                }
-            }
-        }
-    }
-
     fun setCallTimerCallback(callback: CallTimerListener) {
         callTimerListener = callback
     }
@@ -535,21 +522,23 @@ class CallService : Service() {
         }
 
         override fun onSessionStartClose(session: QBRTCSession?) {
-            if (session == WebRtcSessionManager.getCurrentSession()) {
-                CallService.stop(applicationContext)
-            }
+            // empty
         }
 
         override fun onReceiveHangUpFromUser(session: QBRTCSession?, userID: Int?, p2: MutableMap<String, String>?) {
             stopRingtone()
             if (session == WebRtcSessionManager.getCurrentSession()) {
-                if (userID == session?.callerID) {
+                val numberOpponents = session?.opponents?.size
+                if (numberOpponents == ONE_OPPONENT) {
                     currentSession?.let {
                         it.hangUp(HashMap<String, String>())
                         CallService.stop(this@CallService)
                     }
+                }else{
+                    userID?.let {
+                        removeVideoTrack(it)
+                    }
                 }
-                Log.d(TAG, "initiator hung up the call")
             } else {
                 CallService.stop(this@CallService)
             }
@@ -615,9 +604,6 @@ class CallService : Service() {
         override fun onConnectionClosedForUser(session: QBRTCSession?, userID: Int?) {
             Log.d(TAG, "Connection closed for user: $userID")
             shortToast("The user: " + userID + "has left the call")
-            userID?.let {
-                removeVideoTrack(it)
-            }
         }
 
         override fun onStateChanged(session: QBRTCSession?, sessionState: BaseSession.QBRTCSessionState?) {
@@ -627,7 +613,7 @@ class CallService : Service() {
 
     private inner class QBRTCSignalingListener : QBRTCSignalingCallback {
         override fun onSuccessSendingPacket(p0: QBSignalingSpec.QBSignalCMD?, p1: Int?) {
-
+            // empty
         }
 
         override fun onErrorSendingPacket(p0: QBSignalingSpec.QBSignalCMD?, p1: Int?, p2: QBRTCSignalException?) {
diff --git a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/util/ChatPingAlarmManager.kt b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/util/ChatPingAlarmManager.kt
index 701b3459d..6adffca8f 100644
--- a/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/util/ChatPingAlarmManager.kt
+++ b/sample-videochat-kotlin/app/src/main/java/com/quickblox/sample/videochat/kotlin/util/ChatPingAlarmManager.kt
@@ -6,6 +6,7 @@ import android.content.BroadcastReceiver
 import android.content.Context
 import android.content.Intent
 import android.content.IntentFilter
+import android.os.Build
 import android.os.Bundle
 import android.os.SystemClock
 import android.util.Log
@@ -53,10 +54,17 @@ object ChatPingAlarmManager {
      * @param context
      */
     fun onCreate(context: Context) {
+        var intentFlag = 0
+
         this.context = WeakReference(context)
         context.registerReceiver(alarmBroadcastReceiver, IntentFilter(PING_ALARM_ACTION))
         alarmManager = context.getSystemService(Context.ALARM_SERVICE) as AlarmManager
-        pendingIntent = PendingIntent.getBroadcast(context, 0, Intent(PING_ALARM_ACTION), 0)
+
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
+            intentFlag = PendingIntent.FLAG_IMMUTABLE
+        }
+
+        pendingIntent = PendingIntent.getBroadcast(context, 0, Intent(PING_ALARM_ACTION), intentFlag)
         val trigger = SystemClock.elapsedRealtime() + PING_INTERVAL
         alarmManager.setInexactRepeating(AlarmManager.ELAPSED_REALTIME_WAKEUP, trigger, PING_INTERVAL, pendingIntent)
     }
diff --git a/sample-videochat-kotlin/app/src/main/res/values/strings.xml b/sample-videochat-kotlin/app/src/main/res/values/strings.xml
index 96ab7e661..bc9947e70 100644
--- a/sample-videochat-kotlin/app/src/main/res/values/strings.xml
+++ b/sample-videochat-kotlin/app/src/main/res/values/strings.xml
@@ -160,7 +160,7 @@
 
     <!--Call Settings-->
     <string name="pref_answer_time_interval_key">answer_time_interval</string>
-    <string name="pref_answer_time_interval_default_value">60</string>
+    <string name="pref_answer_time_interval_default_value">30</string>
     <string name="pref_disconnect_time_interval_key">disconnect_time_interval</string>
     <string name="pref_disconnect_time_interval_default_value">10</string>
     <string name="pref_dialing_time_interval_key">Dialing_time_interval</string>
@@ -215,5 +215,6 @@
     <string name="error_max_opponents_count">You can select up to %d opponents</string>
     <string name="error_permission_video">You should allow Camera permission</string>
     <string name="error_permission_audio">You should allow Microphone permission</string>
+    <string name="error_get_permission">Error getting permissions</string>
 
 </resources>
\ No newline at end of file
diff --git a/sample-videochat-kotlin/build.gradle b/sample-videochat-kotlin/build.gradle
index d2e7db27a..cbe1ad7e0 100644
--- a/sample-videochat-kotlin/build.gradle
+++ b/sample-videochat-kotlin/build.gradle
@@ -1,22 +1,19 @@
 buildscript {
     repositories {
         google()
-        jcenter()
+        mavenCentral()
     }
 
     dependencies {
-        classpath 'com.android.tools.build:gradle:3.2.0'
-        classpath 'com.google.gms:google-services:4.1.0'
+        classpath 'com.android.tools.build:gradle:4.2.2'
+        classpath 'com.google.gms:google-services:4.3.10'
     }
 }
 
 allprojects {
     repositories {
         google()
-        jcenter()
-        maven {
-            url "https://github.com/QuickBlox/quickblox-android-sdk-releases/raw/master/"
-        }
+        mavenCentral()
     }
 }
 
@@ -26,32 +23,22 @@ ext {
     lintAbortOnError = false
 
     // QuickBlox SDK version
-    qbSdkVersion = '3.9.2'
+    qbSdkVersion = '3.9.15'
 
     //Firebase
-    firebaseCoreVersion = '16.0.8'
-
-    //Glide
-    glideVersion = '3.6.1'
+    firebaseCoreVersion = '20.1.2'
 
     //Material
-    materialVersion = '1.0.0'
+    materialVersion = '1.5.0'
 
     //RobotoTextView
     robotoTextViewVersion = '4.0.0'
 
     //Android X
-    fragmentAndroidXVersion = '1.0.0'
-    lifecycleViewmodelAndroidXVersion = '1.0.0'
-    coreKtxVersion = '1.0.1'
-
-    //Crashlytics
-    crashlyticsVersion = '2.9.5'
-
-    //Fabric
-    fabricToolsVersion = '1.27.0'
+    fragmentAndroidXVersion = '1.4.1'
+    lifecycleViewmodelAndroidXVersion = '2.4.1'
+    coreKtxVersion = '1.7.0'
 
     //Kotlin
-    kotlinGradlePluginVersion = '1.2.71'
-    kotlinReflectVersion = '1.2.71'
+    kotlinGradlePluginVersion = '1.5.31'
 }
\ No newline at end of file
diff --git a/sample-videochat-kotlin/gradle/wrapper/gradle-wrapper.jar b/sample-videochat-kotlin/gradle/wrapper/gradle-wrapper.jar
index f6b961fd5..758de960e 100644
Binary files a/sample-videochat-kotlin/gradle/wrapper/gradle-wrapper.jar and b/sample-videochat-kotlin/gradle/wrapper/gradle-wrapper.jar differ
diff --git a/sample-videochat-kotlin/gradle/wrapper/gradle-wrapper.properties b/sample-videochat-kotlin/gradle/wrapper/gradle-wrapper.properties
index 9a4163a4f..4d9ca1649 100644
--- a/sample-videochat-kotlin/gradle/wrapper/gradle-wrapper.properties
+++ b/sample-videochat-kotlin/gradle/wrapper/gradle-wrapper.properties
@@ -1,5 +1,5 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-4.6-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.7.1-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists