Payment Verification (LUD-21)

Payment Verification provides cryptographic proof that a payment was settled. This enables non-custodial verification of Lightning payments.

Why It Matters

Traditional Lightning payments require trust — when you pay someone, you get a preimage as proof, but verifying that the recipient actually received the funds requires trust in the payment processor. With Payment Verification:

• Trustless confirmation — cryptographic proof the payment reached its destination
• Non-custodial verification — verify without relying on a third party
• Agent-friendly — perfect for autonomous systems that need settlement proof
• Dispute resolution — undeniable evidence for commercial transactions

How It Works

Payment Verification works by having the recipient server provide a verification endpoint that returns a cryptographic signature proving the payment was received.

Flow Overview

1. Sender makes a payment and receives a preimage
2. Sender requests verification from the recipient's server
3. Server returns a signed message confirming receipt
4. Sender can verify the signature independently

Server Response

When responding to the LNURL request, include verification capability:

{
  "callback": "https://domain.com/lnurlp/user/callback",
  "minSendable": 1000,
  "maxSendable": 100000000000,
  "metadata": "[[\"text/plain\",\"Pay user\"]]",
  "tag": "payRequest",
  "payerData": {
    "name": { "mandatory": false },
    "email": { "mandatory": false }
  },
  "nostrPubkey": "npub1...",
  "allowsNostr": true
}

Verification Endpoint

After payment, the sender can verify:

GET /lnurlp/user/verify/{payment_hash}

Response:

{
  "status": "OK",
  "settled": true,
  "preimage": "abc123...",
  "signature": "...",
  "pubkey": "..."
}

Use Cases

Agent Payments

AI agents can verify payments programmatically:

async function verifyPayment(domain: string, user: string, hash: string) {
  const response = await fetch(
    `https://${domain}/lnurlp/${user}/verify/${hash}`
  );
  const data = await response.json();

  if (data.settled) {
    // Verify signature against known pubkey
    return verifySignature(data.signature, data.pubkey, hash);
  }
  return false;
}

E-commerce

Online stores can confirm payment before shipping without trusting a payment processor.

Escrow Services

Third parties can independently verify that both sides of a transaction completed.

Implementation Notes

• The verification endpoint should be rate-limited
• Signatures should use standard cryptographic schemes (secp256k1)
• Payment data should be persisted for the verification window
• Consider privacy implications of exposing payment hashes