A plan can be purchased by a user to obtain points. Those points can then be used to call specific API endpoints. At the backend it is possible to set a specific cost for each route. Every plan has a name, description, price and points. The developer app contains already a possibility to buy those plans.
To enable payments you need to setup a payment provider (i.e. paypal). Through the payment provider the user can purchase such plans. Please take a look at the manual to see how to setup a payment provider: