"error": "InvalidRegistration" while sending push notifications
I'm not familiar with Xamarin. But I worked with FCM a lot.
I think you are getting wrong token. Using deviceToken
won't work with push notification from FCM. I did a search and maybe you have to get it from
var fcmToken = FirebaseInstanceId.Instance.Token;
More detail: https://learn.microsoft.com/en-us/xamarin/android/data-cloud/google-messaging/remote-notifications-with-fcm?tabs=macos