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:
- Access your list of enabled APIs in the Google Developers Console .
- From the project drop-down, choose the project that contains your Hangouts app.
- In the list of Enabled APIs, find the Google+ Hangouts API, then press the gear icon () to the right of the service name to open the API configuration page.
- Locate the Additional OAuth scopes field, then copy and paste
this scope into the field:
- Press Save.