The telephone and billing APIs provide access to the user's Google Voice balance and allow applications to place calls on the user's behalf, possibly costing them money. As a result some methods will only work if the user has granted access via an OAuth scope that the user must agree to when starting the application. Here are the steps to add the scope to your application:
- Open the Google Developers Console.
- Choose the project that contains your Hangout app.
- Choose APIs & auth, find Google+ Hangouts API, then click on the gear icon () to the right of that service name. to get to the settings screen.
- Check This application requires additional OAuth 2.0 scopes. This opens a field.
- Copy and paste this scope into the field:
- Click Save.