Kind 9321: Nutzap

Overview

A Nutzap event (Kind 9321) is used to send P2PK Cashu tokens to Nostr users. It contains Cashu token proofs that are P2PK-locked to the recipient's specified public key. Nutzaps function as a Nostr-native payment mechanism where the payment itself serves as the receipt.

Specification

Property	Value
Kind Number	9321
Event Range	Regular
Defined in	NIP-61

Content Format

The content field contains an optional comment or message accompanying the Nutzap.

Tags

Tag Name	Description	Format	Required
proof	Token proof P2PK-locked to recipient	["proof", "<json-token-proof>"]	Yes
u	URL of the mint	["u", "<mint-url>"]	Yes
e	Event being nutzapped (if any)	["e", "<nutzapped-event-id>", "<relay-hint>"]	No
p	Nostr public key of the recipient	["p", "<recipient-pubkey>"]	Yes

Client Behavior

Senders should:

1. Fetch the recipient's Kind 10019 event to identify trusted mints and the P2PK public key
2. Mint/swap ecash on one of the recipient's listed mints
3. P2PK-lock to the recipient's specified public key (prefixed with "02")
4. Publish the Nutzap event to the relays specified in the recipient's Kind 10019

Recipients should:

1. Monitor their relays for Kind 9321 events that p-tag them
2. Filter for events with u tags matching mints they trust
3. Only process events since the most recent Kind 7376 event they've created
4. Swap received tokens into their wallet
5. Create a Kind 7376 event to record the redemption

Relay Behavior

Relays simply store and serve these events, with no special behavior required.

Use Cases

• Tipping content creators
• Paying for services or goods through Nostr
• Transferring value in a Nostr-native way
• Providing monetization for content and interactions

Example

{
  "id": "2bf3df19ebb911f6aa29a77aa8e20508d4d379211da4c6018fab23cef288a058",
  "pubkey": "4e1d0aa792db0e9d07ddf3870d8039de67bd922479302f0d988e0259534c894b",
  "created_at": 1683123456,
  "kind": 9321,
  "content": "Thanks for this great idea.",
  "tags": [
    ["proof", "{\"amount\":1,\"C\":\"02277c66191736eb72fce9d975d08e3191f8f96afb73ab1eec37e4465683066d3f\",\"id\":\"000a93d6f8a1d2c4\",\"secret\":\"[\\\"P2PK\\\",{\\\"nonce\\\":\\\"b00bdd0467b0090a25bdf2d2f0d45ac4e355c482c1418350f273a04fedaaee83\\\",\\\"data\\\":\\\"02eaee8939e3565e48cc62967e2fde9d8e2a4b3ec0081f29eceff5c64ef10ac1ed\\\"}]\"}" ],
    ["u", "https://stablenut.umint.cash"],
    ["e", "7fc68c564ce4b6ba3fae4dbe0fc9c3f3e11d3048df1424ca5a71f2508dfbf994", "wss://relay.example.com"],
    ["p", "e9fbced3a42dcf551486650cc752ab354347dd413b307484e4fd1818ab53f991"]
  ],
  "sig": "6e8def15e19c84b918ac26c473de935c07aafcaed9a2b0b4544a5fb148d94f6e5fad1efe3a20a2128a6b8bb7e4ca0a6398882367e28cbf61e7e9e2c1aa97e254"
}

References

• NIP-61: Nutzaps
• NIP-60: Wallet Event
• NIP-65: Relay List Metadata
• Cashu NUT-11 (P2PK)
• Cashu NUT-12 (DLEQ Proofs)

Related Kinds

• Kind 10019: Nutzap Informational - Configuration for receiving Nutzaps
• Kind 7376: Nutzap Redemption - Records Nutzap redemption

Notes

• Clients MUST prefix the public key they P2PK-lock with "02" for nostr<>cashu compatibility
• Tokens must be sent to one of the mints explicitly listed in the recipient's Kind 10019 event
• Observer clients verifying Nutzaps should check that:
  • The receiving user has issued a Kind 10019 tagging the mint
  • The token is locked to the pubkey listed in the Kind 10019
  • The mint URL in the u tag matches one listed in the Kind 10019
  • The DLEQ proof of the tokens is valid (can be verified offline)