I have a problem, I cannot write to the Firebase Realtime console, i dont know where is the probelm

my code

public class MainActivity extends AppCompatActivity {
    public static final String ANONYMOUS = "anonymous";
    //create an view objects
    private Button textsenden;
    private EditText text;
    private ImageButton bild;
    private MessageAdapter messageAdapter;
    private ListView mListView;
    private String mUserName;
    //instance the Firebase
    private FirebaseDatabase mFirebaseDatabase;
    private DatabaseReference mMessageDatabaseReference;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mUserName = ANONYMOUS;
        mFirebaseDatabase = FirebaseDatabase.getInstance();
        mMessageDatabaseReference = mFirebaseDatabase.getReference().child("messages");

        textsenden = (Button)findViewById(R.id.text_senden);
        text = (EditText)findViewById(R.id.text_schreiben);
        bild = (ImageButton) findViewById(R.id.bildwehlen);
        mListView = (ListView)findViewById(R.id.list_view);

        List<Message> list = new ArrayList<>();
        messageAdapter = new MessageAdapter(this, R.layout.nachrichtview, list);
        mListView.setAdapter(messageAdapter);

        textsenden.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Message message = new Message(text.getText().toString(), mUserName, null);
                mMessageDatabaseReference.push().setValue(message);
               text.setText("");

            }
        });
    }
}

My Realtime ruls

{
  "rules": {
    ".read": true, 
    ".write": true 
  }
}