I can zap again. Couldn't zap for days (or weeks?). Even with a valid NWC string. Problem was, something changed about the Alby browser extension. Had to delete keys, set it up again and re-login to all Nostr apps. Found out after 30 minutes of trial and error investigation.

This doesn't help at all to build trust in your products. That's a finance-related function. Test more. Don't break things. Don't just vibe code.