Getting 'User does not have Permission to access this object. Code: -13021 HttpResult: 403' error. Please see details

I am trying to download some images from FirebaseStorage.

Though I am authenticating user through google, I'm still getting this error:

E/StorageException: StorageException has occurred. User does not have permission to access this object. Code: -13021 HttpResult: 403

when trying to download the images.

Here's the rules:

service firebase.storage {
  match /b/appname-e3a12.appspot.com/o {
    match /{allPaths=**} {
      allow read, write;
    }
  }
}

Please let me know what's wrong here.

Has anybody got answer for this?

Sorry if question seems to be badly formatted. I'm still a beginner!