Receiver side for marking messages as delivered.

ReceiverMarkAsDelivered.java

//Receiver Side
public class FirebaseMessagingServiceEx extends FirebaseMessagingService {
    @Override
    public void onMessageReceived(RemoteMessage remoteMessage) {
        try {
            JSONObject sendBird = new JSONObject(remoteMessage.getData().get("sendbird"));
            JSONObject channel = (JSONObject) sendBird.get("channel");
            String channelUrl = (String) channel.get("channel_url");

            //Mark the Message as Delivered
            SendBird.markAsDelivered(channelUrl);
        } catch (JSONException e) {
            e.printStackTrace();
        }
    }
}