AltZap Receipt (Kind 9521)

A kind 9521 AltZap Receipt is what the recipient's LNURL server publishes once an invoice is paid. It is the public proof that a zap happened, like NIP-57's kind 9735.

The full definition — tags, the identity tag matrix and how to verify a receipt — is in NIP-AZ.

Example

{
  "kind": 9521,
  "content": "",
  "tags": [
    ["p", "<recipient_hex_or_ConnectionKey>", "<platform>", "<handle>"],
    ["P", "<sender_hex_or_ConnectionKey>", "<platform>", "<handle>"],
    ["r", "<resolved_recipient_pubkey>"],
    ["amount", "<settled_milli_units>"],
    ["chain", "flokicoin"],
    ["bolt11", "lnfc10u1..."],
    ["description", "<the original 9520 or 9523, exactly as received>"],
    ["preimage", "<32-byte hex>"]
  ],
  "pubkey": "<lnurl_server_pubkey>",
  "created_at": 1709424000,
  "id": "...",
  "sig": "..."
}

A client trusts a receipt only after checking it: the signature, that the invoice is on the receipt's chain, that the preimage pays the invoice, and that the invoice commits to the embedded request.

r and R are optional. They carry the real Nostr pubkey behind a ConnectionKey, when the LNURL server knows it from an Identity Connection.

Custodial receipts

When Zapf holds a payment at a Fallback Address — the recipient has no Nostr key yet, or their wallet is unreachable — it still publishes the receipt. The sender sees the zap as final; Zapf sweeps the funds once the recipient connects a wallet.