How Lightning zaps work under the hood. A zap is a Bitcoin Lightning payment attached to a Nostr event. Here's the flow: you click "zap" on a note → your client looks up the author's Lightning address (from their profile metadata) → it fetches a BOLT11 invoice from the author's Lightning wallet via their LNURL endpoint → you pay that invoice → the wallet then publishes a special zap receipt event (NIP-57) back to Nostr relays, signed by the wallet, proving the payment happened. Clients then display that zap receipt as a visible "zap" on the note. The money moves over Lightning; the proof of payment lives on Nostr.