Enable Google Drive API & Authorize Client ID

1. In Google Cloud Platform portal, select the same project as where the Service Account was created.
2. Go to Navigation Menu > APIs & Services > Dashboard.
3. Click on ENABLE APIS AND SERVICES.



4. Search for the Google Drive API and enable it.



5. Go to Google Admin and log in with the same Google Account.
6. Click on Security > API controls.
7. In API controls page, click MANAGE DOMAIN WIDE DELEGATION.



8. Click Add new and add the Client ID from Create Google Service Account.



9. Add "https://www.googleapis.com/auth/drive" to OAuth scope and click AUTHORIZE.