The Subscriptions API allows you to grant users permission to stream content and log subscription data.
It is your responsibility to process the billing itself, but you should then notify MassiveMusic of any changes to a user's Subscription to ensure any royalties and usage reporting are correct when delivered to licensors.
The OAuth 1.0 signature base string includes the parameters from the request entity-body if the body is single-part and application/x-www-form-urlencoded. For example, a JSON body should not be included in the base string.
Reference: here