There seem to have been a recent update which requires you to run some additional code in order for it to work on newer android versions. So the code should looks something like:

NotificationCompat.Builder mBuilder = new NotificationCompat.Builder(this, getString(R.string.default_notification_channel_id))
                    .setSmallIcon(R.drawable.ic_challenge)
                    .setContentTitle(messageTitle)
                    .setContentText(messageBody)
                    .setPriority(Notification.PRIORITY_MAX)
                    .setContentIntent(pendingIntent);

            //to show notification do this

            //Sets ID for the notification

            int mNotificationId = (int) System.currentTimeMillis();
            NotificationManager mNotifyMgr = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);

            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O)
            {
                String channelId = "Tic-Tac-Toe";
                NotificationChannel channel = new NotificationChannel(
                        channelId,
                        "Tic-Tac-Toe",
                        NotificationManager.IMPORTANCE_HIGH);
                mNotifyMgr.createNotificationChannel(channel);
                mBuilder.setChannelId(channelId);
            }

            mNotifyMgr.notify(mNotificationId, mBuilder.build());

I’m sending push notifications in my app and want to be able to show them even if the app is already running, so therefore I’m trying to use the onMessageReceived() function. The function runs whenever I send a notification and I can see that the title and body of the notification is correct, so no problems this far. Then I want the notification to pop up on the users device, but for some reason I just can’t get it to work. I have looked at numerous sites and stackoverflow questions and all code basically looks the same, so it’s a bit confusing why it doesn’t work for me.

 @Override
    public void onMessageReceived(@NonNull RemoteMessage remoteMessage) {
        super.onMessageReceived(remoteMessage);

        String messageTitle = remoteMessage.getNotification().getTitle();
        String messageBody = remoteMessage.getNotification().getBody();
        System.out.println("TITLE_IS: " + messageTitle);
        System.out.println("MESSAGE_BODY: "+ messageBody);

        NotificationCompat.Builder mBuilder = new NotificationCompat.Builder(this, getString(R.string.default_notification_channel_id))
                .setSmallIcon(R.mipmap.ic_launcher)
                .setContentTitle(messageTitle)
                .setContentText(messageBody);

        //Sets ID for the notification
        int mNotificationId = (int) System.currentTimeMillis();
        

        NotificationManager mNotifyMgr = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
        mNotifyMgr.notify(mNotificationId, mBuilder.build());

        System.out.println("Everything went fine");
    }

It never prints the last line (“Everything went fine”), but also don’t give an error so it seems it works even though it didn’t. What is the problem and how do I fix it?