relays store zap receipts (kind 9735)

ln url providers that support nostr accept a prepared and signed zap request (kind 9734) from the caller to the callback to generate the invoice to be paid. your client typically acts as this client. once invoice paid, lnurl provider credits your custodial account and should then issue the zap receipt to relays referenced in the zap request.

see NIP 57, and LUDs 6, 12, 16