Firebase FCM token - When to send to server?

Question

Okay so I have an app which on first start takes you through a few welcoming slides, then takes you to a login/register page and then to MainActivity.

I

Answer 1

December 2020 update : Using the new Firebase SDK (21.0.0) you can get it by overriding onNewToken() method :

@Override
public void onNewToken(@NonNull String s) {
    super.onNewToken(s);
    sendRegistrationToServer(s);
}

Or by FirebaseInstallations.getInstance() within your scope :

FirebaseInstallations.getInstance().getToken(false).addOnCompleteListener(new OnCompleteListener() {
          @Override
          public void onComplete(@NonNull Task task) {
              if(!task.isSuccessful()){
                  return;
              }
              // Get new Instance ID token
              String token = task.getResult().getToken();

          }
      });