diff --git a/android/src/main/kotlin/io/vinicius/appodeal_flutter/AppodealFlutterPlugin.kt b/android/src/main/kotlin/io/vinicius/appodeal_flutter/AppodealFlutterPlugin.kt
index 29b0fbd..d7c9eb4 100644
--- a/android/src/main/kotlin/io/vinicius/appodeal_flutter/AppodealFlutterPlugin.kt
+++ b/android/src/main/kotlin/io/vinicius/appodeal_flutter/AppodealFlutterPlugin.kt
@@ -85,15 +85,16 @@ class AppodealFlutterPlugin : FlutterPlugin, MethodCallHandler, ActivityAware {
         val adTypes = args["adTypes"] as List<Int>
         val testMode = args["testMode"] as Boolean
         val verbose = args["verbose"] as Boolean
+        val userId = args["userId"] as String
 
         // Registering callbacks
         setCallbacks()
 
         val ads = adTypes.fold(0) { acc, value -> acc or getAdType(value) }
+        if (userId != "") Appodeal.getUserSettings(activity).setUserId(userId)
         Appodeal.setTesting(testMode)
         Appodeal.initialize(activity, appKey, ads, hasConsent)
         if (verbose) Appodeal.setLogLevel(Log.LogLevel.verbose)
-
         result.success(null)
     }
 
diff --git a/example/lib/main.dart b/example/lib/main.dart
index 098ac4f..81407c1 100644
--- a/example/lib/main.dart
+++ b/example/lib/main.dart
@@ -43,7 +43,9 @@ class _MyAppState extends State<MyApp> {
       await Appodeal.initialize(
           hasConsent: true,
           adTypes: [AdType.banner, AdType.mrec, AdType.interstitial, AdType.reward, AdType.nonSkippable],
-          testMode: true);
+          testMode: true,
+		      userId: 'User#123', // For S2S rewarded video callbacks
+		  );
 
       setState(() => isAppodealInitialized = true);
     });
diff --git a/lib/src/appodeal.dart b/lib/src/appodeal.dart
index 7ef7f2b..943b2c4 100644
--- a/lib/src/appodeal.dart
+++ b/lib/src/appodeal.dart
@@ -31,7 +31,7 @@ class Appodeal {
   /// also if ads should be presented in test mode [testMode] or not. Always set test mode as `true` during development
   /// or tests.
   static Future<void> initialize(
-      {required bool hasConsent, List<int> adTypes = const [], bool testMode = false, bool verbose = false}) async {
+      {required bool hasConsent, List<int> adTypes = const [], bool testMode = false, bool verbose = false, String userId = ''}) async {
     assert(_androidAppKey != null || _iosAppKey != null, 'You must set at least one of the keys for Android or iOS');
 
     // Register the callbacks
@@ -44,6 +44,7 @@ class Appodeal {
       'adTypes': adTypes,
       'testMode': testMode,
       'verbose': verbose,
+      'userId' : userId,
     });
   }