Checks whether a user's subscription purchase is valid and returns its expiry time.
The URL uses gRPC Transcoding syntax.
The package name of the application for which this subscription was purchased (for example, 'com.some.thing').
The purchased subscription ID (for example, 'monthly001').
The token provided to the user's device when the subscription was purchased.
The request body must be empty.
If successful, the response body contains an instance of
Requires the following OAuth scope: