GoogleService failed to initialize

[From Product Manager @ Google]

You can fix this issue by downloading and copying the google-services.json file for your Android app by following the steps below:

• Select your app/project name and Android packagename from this link and click Continue to Choose and configure services.
• Click Continue to Generate Configuration files.
• Download google-services.json and copy the file to the app/ or mobile/ module directory in your Android project.

If you have previously imported your Google project into Firebase, you can
get the updated google-services.json from the Firebase console under Project Settings.

DO NOT COPY the PROJECT_NUMBER as suggested by one of the other answers since the google_app_id refers to your app within a Project and not the project itself.