Firebase Notification & User Id

Question

I'm using Firebase with an Android app (Auth, Database and Notification).

I'm trying to send notification from an external server (in nodejs) so an user can send a notification to another user.

So the android app memorize a list of UserId (the same ids from Firebase Auth) and then send this list to the nodejs server.

With this list, the server contact the url 'https://fcm.googleapis.com/fcm/send', but Firebase returns me a InvalidRegistration because i'm sending a list of userId and not the list of registration token created by firebase notification.

Should I memorize those tokens or there is a way to send notification with the user id ?

(And when I try with a list of tokens, of course it's working.)

var requestData = {
    "registration_ids": userIds, //Problem is here
    "data": {
      "message": "A message"
     }
  };

  request({
      url: "https://fcm.googleapis.com/fcm/send",
      method: "POST",
      json: true,
      headers: {
          "Authorization": "key=firebaseKey",
          "content-type": "application/json",
      },
      json: requestData
  },
  function(err, response, body) {

  });

Answer 1

Yes, you can. For this you have to register these user Ids instead of device Id token. Then firebase recognized your user Ids.

   @Override
    public void onNewToken(@NonNull String token) {

        super.onNewToken(token);
        Log.d("user_token: ",token);
     

    }