Payment methods live under Settings → Billing → Payment Methods. Add a card and mark it default; the previous default is kept on file as a backup unless you remove it.
If a renewal charge fails, Sadakom retries three times over five days and emails you after each attempt. Your account stays active during retries — access is only paused if all retries fail.
All card data is processed by Stripe; Sadakom never stores full card numbers.