Sender Identity (LUD-18)

Sender Identity allows payers to optionally share information about themselves with the recipient. This enables richer payment experiences and agent attribution.

Why It Matters

Anonymous payments are great for privacy, but sometimes you want the recipient to know who you are:

• Tipping with attribution — let your favorite creator know who their supporters are
• Business payments — attach your company or order info
• Agent identification — AI agents can identify themselves for trust and accountability
• Receipts and records — get proper receipts with your contact info

How It Works

Declaring Supported Fields

When responding to the LNURL request, include a payerData object:

{
  "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 },
    "identifier": { "mandatory": false }
  }
}

Each field can be marked as:

• mandatory: false — optional, sender can choose to share
• mandatory: true — required for the payment to proceed

Available Fields

| Field | Description | Example | |-------|-------------|---------| | name | Sender's name | "Alice Smith" | | email | Sender's email | "alice@example.com" | | identifier | Lightning Address | "alice@wallet.com" | | pubkey | Sender's pubkey | "npub1..." |

Callback with Payer Data

When the sender includes their info, it's passed in the callback:

GET /callback?amount=10000&payerdata={"name":"Alice","identifier":"alice@wallet.com"}

The payerdata is URL-encoded JSON.

Implementation Example

app.get('/lnurlp/:username/callback', async (req, res) => {
  const { amount, payerdata } = req.query;

  let senderInfo = null;
  if (payerdata) {
    try {
      senderInfo = JSON.parse(decodeURIComponent(payerdata));
    } catch (e) {
      // Invalid payer data, continue without it
    }
  }

  // Store sender info with the payment
  const payment = await createPayment({
    recipient: req.params.username,
    amount: parseInt(amount),
    senderName: senderInfo?.name,
    senderEmail: senderInfo?.email,
    senderAddress: senderInfo?.identifier
  });

  const invoice = await generateInvoice(payment);
  res.json({ pr: invoice });
});

For AI Agents

Sender Identity is particularly valuable for agents:

// Agent identifies itself when making payments
const payerData = {
  name: "Research Agent v1.2",
  identifier: "research-agent@mycompany.ai"
};

await payLightningAddress("creator@example.com", 1000, {
  payerData
});

This creates an audit trail and enables recipients to whitelist trusted agents.

Privacy Considerations

• All fields are opt-in from the sender's perspective
• Wallets should clearly show what data will be shared
• Recipients should handle payer data responsibly
• Consider GDPR and other privacy regulations