FirebaseMessaging.onMessage.listen() only working for Notification messages

Question

I am currently working on an application for iOS where I want to send push notifications through Firebase's Cloud Messaging console, and send notifications through https://fcm.googleapis.com/fcm/send via a Java http request. I created an onMessage listener shown here:

FirebaseMessaging.onMessage.listen((RemoteMessage message) {
  print("onMessage listener fired");
  if (message != null) {
    PersonalFirebase.onMessageReceived(message, context, setState, flutterLocalNotificationsPlugin, notificationSettings.authorizationStatus);
  }
});

This listener is successfully fired if I send a message through the Firebase console in my project, however nothing happens if I attempt to send a data message through an HTTP request even when I get a 200 response code. For reference, here is the payload I am sending to the http request in Java:

    JSONObject values = new JSONObject();
    values.put("action", "show_message");
    values.put("title", "showMessageFunction");
    values.put("message", "Testing showMessage function");
    values.put("channel", "1");
    
    JSONObject parentData = new JSONObject();
    parentData.put("data", values);
    
    JSONObject message = new JSONObject();
    message.put("to", to);
    message.put("data", parentData); 
    

Basically my question is as follows: does FirebaseMessaging.onMessage only work for Notifications sent through the Firebase console. If so, is there an alternative to FirebaseMessaging.onMessage for data messages through a https://fcm.googleapis.com/fcm/send http request?

Let me know if there is anything else I can add to help.

Solution

All we had to do was add message.put("content_available", true); to the end of our message JSONObject. Further information can be found here.