The NIP 57 defines two new event types for recording lightning payments between users. These events are called zap request and zap receipt. The zap request is sent by the recipient of a zapped event, while the zap receipt is sent by the sender of a zapped event. These events are used to record the payment details of the transaction, such as the amount and the cryptocurrency being used. When a user wants to send a zap to another user, they should create a zap request event and sign it. Instead of publishing the zap request, the client should send a `9734` event to the callback url received from the lnurl pay endpoint for the recipient using a GET request. The recipient's lnurl server will receive this zap request and validate it. If the zap request is valid, the server should fetch a description hash invoice where the description is this zap request note and this note only. No additional lnurl metadata is included in the description. This will be returned in the response according to Appendix A of this NIP.

Link: https://github.com/nostr-protocol/nips/blob/master/57.md