Subscriptions
Billing and subscriptions are separated concepts. Though it is possible to create a subscription based on an online payment, it is also possible to create subscriptions with no associated charge. The plaftorm manages a payment balance on renewal if necessary. That balance can be paid online or off-line. If you like the platform subscription-based access control features but prefer to manage all payments outside the platform, you can do so easily.
Provider and subscriber
Providers are profiles that manage subscription plans. Other profiles on the platform can subscribe to those provider plans. This profiles are thus called Subscribers whith regards to the subscription relationship.
Thus the API is separated into two, depending on which side of the relationship, subscribers or providers, a profile resides.
Subscriber API
The number of endpoints for a subscriber are limited and straightforward to understand so we will start there.
Provider API
A provider must create a plan in order to have subscribers. The REST APIs for plans are pretty straightforward so we won't spend much time on them here.
A provider can list subscribers accross all its plans, list subscriptions that are active, churned, or active but with no activity from users. That last one can help a product identify subscribers potentially churning when their subscription is over.