What happens if a payment fails?

Stripe retries it over the following days and emails you each time. During those retries your account keeps working: locking someone out over a card that bounced once is how a recoverable payment becomes a cancellation.

If every retry fails the subscription ends, and access narrows to Settings and Support so you can fix the card or export your data. Adding a working card and paying the outstanding invoice restores everything, with your data exactly as you left it.