To access Google Sign-In, you’ll need to make sure to register your application.
You don’t need to include the google-services.json file in your app unless you are using Google services that require it. You do need to enable the OAuth APIs that you want, using the Google Cloud Platform API manager. For example, if you want to mimic the behavior of the Google Sign-In sample app, you’ll need to enable the Google People API.
Make sure you’ve filled out all required fields in the console for OAuth consent screen. Otherwise, you may encounter