Once your customer has decided to start the subscription this endpoint will create the recurring billing request.
Since this is a server-to-server communication, if you have a mobile or Web client that communicates with your REST API, you must have a new endpoint E.g. /create-subscription or reuse an existing endpoint. This endpoint will be responsible for making the recurring billing API call to hitpay.
For the request to save car: it's similar to this API with save_card set to true and plan_id should be null