POST /api/ucp/checkout-sessions — Create a checkout session.
POST /api/invoices — Create a new invoice.
POST /api/subscriptions — Create a new subscription.
GET /api/ucp/checkout-sessions?id= — Get a checkout session.
POST /api/payments/verify-np — Verify a Nanda Point payment.
DELETE /api/ucp/checkout-sessions/:id — Cancel a checkout session.