You do not need to declare next_payment_date, unless you know the date for next_payment_date. We do not validate on next_payment_date.
However, it is something that is visible on the customers agreement screen in the app, if you have filled in the "next_payment_date" and if the first payment date > current date.
We have just two validations for subscription payments:
- The customer should have 8 days to assess the payment, so if you send a subscription payment today, the due date could be 23/01 or later (i.e. the 8 day rule).
- You can send a subscription payments to us max. 32 days before the due date.
So for the next month/period you need to create new payment requests.