why every first time I open my android app it says Firebase Database error: permission denied code example

Example: Uncaught (in promise) Error: PERMISSION_DENIED: Permission denied at Repo.ts:632

firebase.auth().signInAnonymously().catch(function(error) {
  // Handle Errors here.
  var errorCode = error.code;
  var errorMessage = error.message;
  // ...
});