diff --git a/config/siasn-api.php b/config/siasn-api.php
index dc5d615..7adef47 100644
--- a/config/siasn-api.php
+++ b/config/siasn-api.php
@@ -2,6 +2,7 @@
 
 return [
 
+    // Supported mode: "production", "training"
     'mode' => env('SIASN_MODE', 'training'),
 
     'apim' => [
diff --git a/src/Helpers/Config.php b/src/Helpers/Config.php
index b57aff5..bf3640d 100644
--- a/src/Helpers/Config.php
+++ b/src/Helpers/Config.php
@@ -85,7 +85,7 @@ public static function getConst(): object
     /**
      * Get mode.
      */
-    public static function getApimTokenAge(): string
+    public static function getApimTokenAge(): ?int
     {
         return config('siasn-api.token_age.apim');
     }
@@ -93,7 +93,7 @@ public static function getApimTokenAge(): string
     /**
      * Get mode.
      */
-    public static function getSsoTokenAge(): string
+    public static function getSsoTokenAge(): ?int
     {
         return config('siasn-api.token_age.sso');
     }