firebase messaging not working with android version 6 (api 23)

Question

i've applied this tutorial to work with fcm: https://learn.microsoft.com/en-us/xamarin/android/data-cloud/google-messaging/remote-notifications-with-fcm?tabs=windows . it worked for android version 10 and 9. when i tested it on android 6, it didn't work. the logs don't even work. for example:

 var logTokenButton = FindViewById<Button>(Resource.Id.logTokenButton);
            logTokenButton.Click += delegate { Log.Debug(TAG, "InstanceID token: " + FirebaseInstanceId.Instance.Token);
           
            };

log.debug doesn't give any result. though when i added toast to see if there is a token value, i got one. what might be wrong? thanks in advance.