FCM showing duplicate notification when app is in background

Question

I implemented FCM in my project. Push notification is working as expected, onMessageReceived is called when a notification is received. This is true when app is in the foreground.

However, when the app is in the background, the system tray always display a duplicate notification when one arrives (e.g. when Notification A is received, system tray display 2 Notification A)

How to fix this?

EDIT: added code

I extended FirebaseMessagingService class and have this in the onMessageReceived method

This is the only part in the project where I used NotificationManager.

Also, I tried to add a log on this method. onMessageReceived is called when app is in foreground. It doesn't get called when app is in background

@Override
public void onMessageReceived(RemoteMessage remoteMessage)
{
    RemoteMessage.Notification notification = remoteMessage.getNotification();

        Intent intent = new Intent(this, MainActivity.class);
        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        PendingIntent pendingIntent = PendingIntent.getActivity(this, 0 /* Request code */, intent,
                PendingIntent.FLAG_ONE_SHOT);

        String title = notification.getTitle();
        String message = notification.getBody();

        NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(this)
                .setSmallIcon(R.mipmap.ic_launcher)
                .setContentTitle(title)
                .setContentText(message)
                .setAutoCancel(true)
                .setDefaults(Notification.DEFAULT_SOUND | Notification.DEFAULT_VIBRATE)
                .setContentIntent(pendingIntent);


        NotificationManager notificationManager =
                (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);

        notificationManager.notify(0, notificationBuilder.build());
}

Answer 1

Same problem. I modified AndroidManifest.xml because i was requesting permissions to old GCM like this...

<uses-permission android:name="mypackage.permission.C2D_MESSAGE" />
<uses-permission android:name="com.google.android.c2dm.permission.RECEIVE" />

<permission
    android:name="mypackage.permission.C2D_MESSAGE"
    android:protectionLevel="signature" />

So, removing it from manifest and uninstalling and reinstalling the app my problem was solved.