If you are still using old style to get FireBase token, it is time to change it.
Old way
String token = FirebaseInstanceId.getInstance().getToken();
New way
FirebaseInstanceId.getInstance().getInstanceId()
.addOnCompleteListener(new OnCompleteListener<InstanceIdResult>() {
@Override
public void onComplete(@NonNull Task<InstanceIdResult> task) {
if (!task.isSuccessful()) {
Log.w("FB token e: ", "getInstanceId failed", task.getException());
return;
}
// Get new Instance ID token
String token = task.getResult().getToken();
Log.d("FB token", token);
if (!token.equals("")) {
// send to your server }
}
});