what causes "permission denied"-message with FIREBASE and FLUTTER

Question

I've got the error

'W/SyncTree(31625): Listen at /address failed: DatabaseError: Permission denied'

while sending a request to firebase with an anonymous firebase user and without fancy firebase database rules :) . ..and i want to find out what causes this message.

EDIT: error is the same with an existing user, means user signIn seems to work but accessing database not.

What i've done so far:

• Set up firebase (including adding google_service.json, dependencies in pubspec.yaml) - works so far

• creating login as follows (like in example from google link):

  Future<String> _testSignInAnonymously() async {
    final FirebaseUser user = await _auth.signInAnonymously();
    assert(user != null);
    assert(user.isAnonymous);
    assert(!user.isEmailVerified);
    assert(await user.getIdToken() != null);
    assert(user.providerData.length == 1);
    assert(user.providerData[0].providerId == 'firebase');
    assert(user.providerData[0].uid != null);
    assert(user.providerData[0].displayName != null);
    assert(user.providerData[0].photoUrl == null);
    assert(user.providerData[0].email != null);
  
    final FirebaseUser currentUser = await _auth.currentUser();
    print(currentUser.uid);
    print(currentUser.isAnonymous);
    assert(user.uid == currentUser.uid);
  
    return 'signInAnonymously succeeded: $user';
  }
  

• the print statement provides a userId (and this id is also in firebase auth section) --> seems to me that i've got an logged in user

• implement kind of initialization like in the google example (link):

  Future<void> main() async {
    final FirebaseApp app = await FirebaseApp.configure(
      name: 'mydbName',
      options: const FirebaseOptions(
         googleAppID: 'myAppId',
         apiKey: 'myApiKey',
         databaseURL: 'myUrl',
      ),
   );
   runApp(new MyApp(app));
  }
  

• on another stateful widget in state i try to request some firebase data:

  void initState() {
    final FirebaseDatabase database = new FirebaseDatabase(app: widget.app);
    database.reference().child('address').once().then((DataSnapshot snapshot) {
      print('Connected to database and read ${snapshot.value}');
    });
    super.initState();
  }
  

• i've removed all rules in firebase except:

  ".read": "auth != null",
  ".write": "auth != null",
  

• i use an SHA-1 certificate/fingerprint in my firebase android app

• i use the same firebase database with an firebase ios app without any problem while using anonymous users

What i need:

I need some hint how to find out if there's any problem with that initialization code or with the user login or something else

Answer 1

It seems the database is not correctly addressed in FirebaseApp.configure(

FirebaseDatabase.instance.reference().child(...)

would use the default database of the project configured in google-services.json