Q: Receive system tray notification when app killed on Android When my app gets killed, I can't receive notifications I set from my app server.
Previous my gradle was as such:
implementation "com.google.firebase:firebase-messaging:17.0.0"
implementation "com.google.firebase:firebase-invites:16.0.0"

Wih this gradle config I was able to receive notification in foreground, background even when app is swiped
I updated my forebase-messanging so here's my new gradle with firebase-messanging:
implementation "com.google.firebase:firebase-messaging:18.0.0"

Here's my current Service class after update
public class MyService extends FirebaseMessagingService
{
public static final String ACTION = "action";
public static final String EXTRA_DATA = "extra_data";
public static final String MESSAGE = "message";
private RemoteMessage.Notification mNotification;

@Override
public void onNewToken(String refreshedToken) {
    super.onNewToken(refreshedToken);
    LOGE(TAG, "Refreshed token: " + refreshedToken);

}

@Override
public void onMessageReceived(RemoteMessage remoteMessage) {
    super.onMessageReceived(remoteMessage);
    String from = message.getFrom();
    mNotification = message.getNotification();
    Map<String, String> data = message.getData();
    LOGE(TAG, "Received FCM message from : " + from + " data : " + data);
}
}

With this new version, it it still possible to receive notifications in system-tray when app is swiped ? If so, any ideas ?

A: Have you defined service class in your manifest like this?:
<service
    android:name=".MyService"
    android:exported="false">
    <intent-filter>
        <action android:name="com.google.firebase.MESSAGING_EVENT" />
    </intent-filter>
</service>

and if the problem persists even after that. add below method and call it from your onMessageReceived THis should resolve any kind of problems.
    private void sendNotification(String messageBody) {
        Intent intent = new Intent(this, MainActivity.class); // Put your own launcher Activity
        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        PendingIntent pendingIntent = PendingIntent.getActivity(this, 0 /* Request code */, intent,
                PendingIntent.FLAG_ONE_SHOT);

        String channelId = getString(R.string.default_notification_channel_id);
        Uri defaultSoundUri = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);
        NotificationCompat.Builder notificationBuilder =
                new NotificationCompat.Builder(this, channelId)
                        .setSmallIcon(R.drawable.ic_stat_ic_notification)
                        .setContentTitle(getString(R.string.fcm_message))
                        .setContentText(messageBody)
                        .setAutoCancel(true)
                        .setSound(defaultSoundUri)
                        .setContentIntent(pendingIntent);

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

        // Since android Oreo notification channel is needed.
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            NotificationChannel channel = new NotificationChannel(channelId,
                    "Channel human readable title",
                    NotificationManager.IMPORTANCE_DEFAULT);
            notificationManager.createNotificationChannel(channel);
        }

        notificationManager.notify(0 /* ID of notification */, notificationBuilder.build());
}

The above method is taken from Firebase repository.

A: I have experienced the same on certain phones e.g. Asus Zenfone. When I swipe the app from the current tasks/apps list, firebase messages are not delivered, all background services/jobs are stopped/never triggered. But on other manufacturers like Samsung, the swiping the app still can receive those messages. 
I think there is no other way except of "whitelisting" your app - user has to do it manually, forgot what it's called in Zenfone.  
