diff --git a/composer.json b/composer.json
index f940e16..2f2b77a 100644
--- a/composer.json
+++ b/composer.json
@@ -12,7 +12,7 @@
   ],
   "prefer-stable": true,
   "require": {
-    "php": ">=5.6"
+    "php": ">=7.0"
   },
   "require-dev": {
     "10up/phpcs-composer": "^3.0",
diff --git a/composer.lock b/composer.lock
index 31791cb..a2b433e 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "9c39d58a367b0054a205ffd85162eb2f",
+    "content-hash": "b4631e7ae4a2f6a3795a92a813440087",
     "packages": [],
     "packages-dev": [
         {
@@ -814,7 +814,7 @@
     "prefer-stable": true,
     "prefer-lowest": false,
     "platform": {
-        "php": ">=5.6"
+        "php": ">=7.0"
     },
     "platform-dev": [],
     "plugin-api-version": "2.6.0"
diff --git a/lib/mailchimp/mailchimp.php b/lib/mailchimp/mailchimp.php
index 478572e..07f9273 100644
--- a/lib/mailchimp/mailchimp.php
+++ b/lib/mailchimp/mailchimp.php
@@ -141,8 +141,9 @@ public function post( $endpoint, $body, $method = 'POST' ) {
 				return new WP_Error( 'mc-subscribe-error', $request->get_error_message() );
 			}
 
-			$body   = json_decode( $request['body'], true );
-			$merges = get_option( 'mc_merge_vars' );
+			$body       = json_decode( $request['body'], true );
+			$merges     = get_option( 'mc_merge_vars' );
+			$field_name = '';
 			foreach ( $merges as $merge ) {
 				if ( empty( $body['errors'] ) ) {
 					// Email address doesn't come back from the API, so if something's wrong, it's that.
diff --git a/mailchimp.php b/mailchimp.php
index d9b5768..5e18821 100644
--- a/mailchimp.php
+++ b/mailchimp.php
@@ -5,7 +5,8 @@
  * Description:       Add a Mailchimp signup form widget to your WordPress site.
  * Version:           1.5.8
  * Requires at least: 2.8
- * Requires PHP:      5.6
+ * Requires PHP:      7.0
+ * PHP tested up to:  8.3
  * Author:            Mailchimp
  * Author URI:        https://mailchimp.com/
  * License:           GPL-2.0-or-later
@@ -69,7 +70,7 @@ function mailchimp_sf_plugin_init() {
 
 	// Remove Sopresto check. If user does not have API key, make them authenticate.
 
-	if ( get_option( 'mc_list_id' ) && get_option( 'mc_merge_field_migrate' ) !== true && mailchimp_sf_get_api() !== false ) {
+	if ( get_option( 'mc_list_id' ) && get_option( 'mc_merge_field_migrate' ) !== '1' && mailchimp_sf_get_api() !== false ) {
 		mailchimp_sf_update_merge_fields();
 	}
 
@@ -126,7 +127,7 @@ function mailchimp_sf_load_resources() {
 		wp_enqueue_script( 'jquery-ui-datepicker' );
 	}
 
-	if ( get_option( 'mc_nuke_all_styles' ) !== true ) {
+	if ( get_option( 'mc_nuke_all_styles' ) !== '1' ) {
 		wp_enqueue_style( 'mailchimp_sf_main_css', home_url( '?mcsf_action=main_css&ver=' . MCSF_VER, 'relative' ), array(), MCSF_VER );
 		wp_enqueue_style( 'mailchimp_sf_ie_css', MCSF_URL . 'css/ie.css', array(), MCSF_VER );
 		global $wp_styles;
@@ -644,6 +645,10 @@ function mailchimp_sf_change_list_if_necessary() {
 	// we *could* support paging, but few users have that many lists (and shouldn't)
 	$lists = $api->get( 'lists', 100, array( 'fields' => 'lists.id,lists.name,lists.email_type_option' ) );
 
+	if ( ! isset( $lists['lists'] ) || is_wp_error( $lists['lists'] ) ) {
+		return;
+	}
+
 	$lists = $lists['lists'];
 
 	if ( is_array( $lists ) && ! empty( $lists ) && isset( $_POST['mc_list_id'] ) ) {
@@ -703,7 +708,7 @@ function mailchimp_sf_change_list_if_necessary() {
  *
  * @param string $list_id List ID
  * @param bool   $new_list Whether this is a new list
- * @return void
+ * @return array
  */
 function mailchimp_sf_get_merge_vars( $list_id, $new_list ) {
 	$api = mailchimp_sf_get_api();
@@ -984,7 +989,7 @@ function mailchimp_sf_merge_submit( $mv ) {
 		$opt_val = isset( $_POST[ $opt ] ) ? map_deep( stripslashes_deep( $_POST[ $opt ] ), 'sanitize_text_field' ) : '';
 
 		// Handle phone number logic
-		if ( 'phone' === $mv_var['type'] && 'US' === $mv_var['options']['phone_format'] ) {
+		if ( isset( $mv_var['options']['phone_format'] ) && 'phone' === $mv_var['type'] && 'US' === $mv_var['options']['phone_format'] ) {
 			$opt_val = mailchimp_sf_merge_validate_phone( $opt_val, $mv_var );
 			if ( is_wp_error( $opt_val ) ) {
 				return $opt_val;
@@ -1265,7 +1270,7 @@ function mailchimp_sf_where_am_i() {
 	// Set defaults
 	$mscf_dirbase = trailingslashit( basename( __DIR__ ) );  // Typically wp-mailchimp/ or mailchimp/
 	$mscf_dir     = trailingslashit( plugin_dir_path( __FILE__ ) );
-	$mscf_url     = trailingslashit( plugins_url( null, __FILE__ ) );
+	$mscf_url     = trailingslashit( plugins_url( '', __FILE__ ) );
 
 	// Try our hands at finding the real location
 	foreach ( $locations as $key => $loc ) {
diff --git a/mailchimp_widget.php b/mailchimp_widget.php
index 50abc7c..f799df0 100644
--- a/mailchimp_widget.php
+++ b/mailchimp_widget.php
@@ -63,7 +63,7 @@ function mailchimp_sf_signup_form( $args = array() ) {
 
 	$sub_heading = trim( get_option( 'mc_subheader_content' ) );
 
-	if ( get_option( 'mc_nuke_all_styles' ) !== true ) {
+	if ( get_option( 'mc_nuke_all_styles' ) !== '1' ) {
 		?>
 	<style>
 		.widget_mailchimpsf_widget .widget-title {
@@ -235,7 +235,7 @@ function mailchimp_sf_signup_form( $args = array() ) {
 			<div class="field-group groups mc_email_options">
 				<ul class="mc_list">
 					<li><input type="radio" name="email_type" id="email_type_html" value="html" checked="checked"><label for="email_type_html" class="mc_email_type"><?php esc_html_e( 'HTML', 'mailchimp_i18n' ); ?></label></li>
-					<li><input type="radio" name="email_type" id="email_type_text" value="text"><label for="email_type_text" class="mc_email_type"><?php esc_html_( 'Text', 'mailchimp_i18n' ); ?></label></li>
+					<li><input type="radio" name="email_type" id="email_type_text" value="text"><label for="email_type_text" class="mc_email_type"><?php esc_html_e( 'Text', 'mailchimp_i18n' ); ?></label></li>
 				</ul>
 			</div>
 		</div>
@@ -465,7 +465,7 @@ function mailchimp_form_field( $data, $num_fields ) {
 	<input type="text" size="18" maxlength="5" value="" name="' . esc_attr( $opt ) . '" id="' . esc_attr( $opt ) . '" class="mc_input" />';
 				break;
 			case 'phone':
-				if ( 'US' === $data['options']['phone_format'] ) {
+				if ( isset( $data['options']['phone_format'] ) && 'US' === $data['options']['phone_format'] ) {
 					$html .= '
 			<input type="text" size="2" maxlength="3" value="" name="' . esc_attr( $opt . '[area]' ) . '" id="' . esc_attr( $opt . '-area' ) . '" class="mc_input mc_phone" />
 			<input type="text" size="2" maxlength="3" value="" name="' . esc_attr( $opt . '[detail1]' ) . '" id="' . esc_attr( $opt . '-detail1' ) . '" class="mc_input mc_phone" />
diff --git a/phpcs-compat.xml b/phpcs-compat.xml
index 343c7f3..0169949 100644
--- a/phpcs-compat.xml
+++ b/phpcs-compat.xml
@@ -14,5 +14,5 @@
 	<exclude-pattern>*/po/*</exclude-pattern>
 
 	<config name="minimum_supported_wp_version" value="6.0"/>
-	<config name="testVersion" value="5.6-"/>
+	<config name="testVersion" value="7.0-"/>
 </ruleset>
diff --git a/phpcs.xml b/phpcs.xml
index 5d56154..4bed1da 100644
--- a/phpcs.xml
+++ b/phpcs.xml
@@ -7,7 +7,7 @@
 	<exclude-pattern>*/tests/*</exclude-pattern>
 
 	<config name="minimum_supported_wp_version" value="6.0"/>
-	<config name="testVersion" value="5.6-"/>
+	<config name="testVersion" value="7.0-"/>
 
 	<!-- Exclude the PHPCompatibilityWP ruleset -->
 	<rule ref="PHPCompatibilityWP">
diff --git a/readme.txt b/readme.txt
index 72dce61..e680f1a 100644
--- a/readme.txt
+++ b/readme.txt
@@ -10,7 +10,7 @@ Add a Mailchimp signup form widget to your WordPress site.
 
 == Description ==
 
-Use the Mailchimp List Subscribe plugin to quickly add a Mailchimp signup form widget to your WordPress 2.8 or higher site. 
+Use the Mailchimp List Subscribe plugin to quickly add a Mailchimp signup form widget to your WordPress 2.8 or higher site.
 
 After installation, you’ll log in with your API key, select your Mailchimp list, choose merge fields and groups, and add the widget to your site.  Typically, installation and setup will take about 5-10 minutes, and absolutely everything can be done via the WordPress Setting GUI, with no file editing at all.
 
@@ -34,7 +34,7 @@ This section describes how to install the plugin and get started using it.
 
 If you have a custom coded sidebar or bells and whistles that prevent enabling widgets  through the WordPress GUI, complete these steps instead.
 
-WordPress v2.8 or higher: 
+WordPress v2.8 or higher:
 ` [mailchimpsf_form] `
 
 If you are adding it inside a php code block, pop this in:
@@ -100,6 +100,7 @@ If your language is not listed above, feel free to create a translation. Here ar
 
 = 1.6.0 =
 * Deprecated function `mailchimpSF_signup_form`. Function `mailchimp_sf_signup_form` should be used instead.
+* Bumps minimum PHP version to 7.0
 
 = 1.5.8 =
 * Fix PHP warning for merge tags.
diff --git a/views/setup_page.php b/views/setup_page.php
index 3e01fb9..884b524 100644
--- a/views/setup_page.php
+++ b/views/setup_page.php
@@ -76,7 +76,7 @@
 
 	<br/>
 	<?php
-	if ( '' !== $user && $user['username'] ) {
+	if ( '' !== $user && isset( $user['username'] ) && $user['username'] ) {
 		?>
 <!--<div class="notes_msg">
 		<strong><?php esc_html_e( 'Notes', 'mailchimp_i18n' ); ?>:</strong>
@@ -233,7 +233,7 @@
 <tr><th colspan="2">Remove Mailchimp CSS</th></tr>
 <tr class="mc-internal-heading"><th><label for="mc_nuke_all_styles"><?php esc_html_e( 'Remove CSS' ); ?></label></th><td><span class="mc-pre-input"></span><input type="checkbox" name="mc_nuke_all_styles" id="mc_nuke_all_styles" <?php checked( get_option( 'mc_nuke_all_styles' ), true ); ?> onclick="showMe('mc-custom-styling')"/><?php esc_html_e( 'This will disable all Mailchimp CSS, so it\'s recommended for WordPress experts only.' ); ?></td></tr>
 </table>
-<?php if ( get_option( 'mc_nuke_all_styles' ) === true ) { ?>
+<?php if ( get_option( 'mc_nuke_all_styles' ) === '1' ) { ?>
 	<table class="widefat mc-widefat mc-custom-styling" id="mc-custom-styling" style="display:none">
 	<?php } else { ?>
 		<table class="widefat mc-widefat mc-custom-styling" id="mc-custom-styling">
@@ -331,7 +331,7 @@
 				<?php
 				$mv = get_option( 'mc_merge_vars' );
 
-				if ( count( $mv ) === 0 || ! is_array( $mv ) ) {
+				if ( ! is_array( $mv ) || count( $mv ) === 0 ) {
 					?>
 					<em><?php esc_html_e( 'No Merge Fields found.', 'mailchimp_i18n' ); ?></em>
 					<?php