Paying with invoice

This guide walks through settling an invoice on-chain using ERC-3009 with a deterministic nonce derived from invoice metadata. The nonce links each payment to its invoice and prevents double payment.

What you'll build

A full invoice lifecycle: the buyer signs an ERC-3009 authorization off-chain, the vendor submits it on-chain, and reconciliation matches the resulting AuthorizationUsed event back to the invoice by deterministic nonce.

Demo

step 1. Invoice issued
        number:  INV-2026-001234
        amount:  5000 USDT0
        dueDate: 2026-04-30

step 2. Buyer signs authorization (off-chain, no gas)
        nonce:     0xa1b2...c3d4 (from invoice metadata)
        signature: 0xf0e9...1234

step 3. Vendor submits transferWithAuthorization
        tx:     0x8f3a...2d41
        amount: 5000 USDT0 transferred to vendor

step 4. Reconciliation
        AuthorizationUsed(nonce=0xa1b2...) → invoice INV-2026-001234
        Transfer event verified for correct amount and parties
        ERP: marked PAID at block 1284371

Overview

Buyer:

─── Buyer ───────────────────────────────────────────
nonce = getInvoiceNonce(invoice)
authorization = { from: buyer, to: vendor, value: amount, nonce, ... }
signature = signTypedData(authorization)
 
// Option A: Buyer submits the transaction directly.
usdt0.transferWithAuthorization(authorization, signature)
 
// Option B: Buyer sends {authorization, signature} to the vendor.
//           The vendor (or a facilitator) submits on the buyer's behalf.

Vendor:

─── Vendor ──────────────────────────────────────────
// If Option B: submit transferWithAuthorization using the buyer's signature
 
// Reconcile via AuthorizationUsed event
on AuthorizationUsed(authorizer, nonce):
    invoice = nonceToInvoice.get(nonce)
    transferLog = receipt.logs.find(Transfer matching invoice.buyer, invoice.vendor, invoice.amount)
    if transferLog:
        erpSystem.markPaid(invoice.id, txHash, settledAt)

Configuration

// config.ts
import { ethers } from "ethers";
 
export const STABLE_TESTNET_RPC = "https://rpc.testnet.stable.xyz";
export const CHAIN_ID = 2201;
export const USDT0_ADDRESS = "0x78Cf24370174180738C5B8E352B6D14c83a6c9A9";
 
export const provider = new ethers.JsonRpcProvider(STABLE_TESTNET_RPC);
 
export const EIP712_DOMAIN = {
  name: "USDT0",
  version: "1",
  chainId: CHAIN_ID,
  verifyingContract: USDT0_ADDRESS,
};
 
export const TRANSFER_WITH_AUTHORIZATION_TYPE = {
  TransferWithAuthorization: [
    { name: "from", type: "address" },
    { name: "to", type: "address" },
    { name: "value", type: "uint256" },
    { name: "validAfter", type: "uint256" },
    { name: "validBefore", type: "uint256" },
    { name: "nonce", type: "bytes32" },
  ],
};
 
export interface Invoice {
  number: string;   // e.g. "INV-2026-001234"
  vendor: string;   // vendor wallet address
  buyer: string;    // buyer wallet address
  amount: bigint;   // amount in USDT0 atomic units (6 decimals)
  dueDate: number;  // Unix timestamp
}

Step 1: Generate a deterministic nonce

Both the buyer and the vendor can independently compute the same nonce from invoice metadata. No external registry is needed.

// nonce.ts
import { ethers } from "ethers";
import { Invoice } from "./config";
 
export function getInvoiceNonce(invoice: Invoice): string {
  return ethers.solidityPackedKeccak256(
    ["string", "address", "address", "uint256", "uint256"],
    [
      invoice.number,
      invoice.vendor,
      invoice.buyer,
      invoice.amount,
      invoice.dueDate,
    ]
  );
}
 
// Example
const invoice: Invoice = {
  number: "INV-2026-001234",
  vendor: "0xVendorAddress",
  buyer: "0xBuyerAddress",
  amount: ethers.parseUnits("5000", 6), // 5,000 USDT0
  dueDate: Math.floor(new Date("2026-04-30").getTime() / 1000),
};
 
const nonce = getInvoiceNonce(invoice);
// Same input always produces the same nonce.
// This nonce is consumed on-chain upon payment, preventing double payment.

Step 2: Sign the authorization (buyer)

The buyer signs an ERC-3009 transferWithAuthorization using the deterministic nonce from Step 1.

// sign-invoice.ts
import { ethers } from "ethers";
import {
  provider,
  EIP712_DOMAIN,
  TRANSFER_WITH_AUTHORIZATION_TYPE,
  Invoice,
} from "./config";
import { getInvoiceNonce } from "./nonce";
 
const buyerWallet = new ethers.Wallet(process.env.BUYER_KEY!, provider);
 
async function signInvoiceAuthorization(invoice: Invoice) {
  const nonce = getInvoiceNonce(invoice);
  const gracePeriod = 30 * 24 * 60 * 60; // 30 days after due date
 
  const authorization = {
    from: invoice.buyer,
    to: invoice.vendor,
    value: invoice.amount,
    validAfter: 0,
    validBefore: invoice.dueDate + gracePeriod,
    nonce,
  };
 
  const signature = await buyerWallet.signTypedData(
    EIP712_DOMAIN,
    TRANSFER_WITH_AUTHORIZATION_TYPE,
    authorization
  );
 
  return { authorization, signature };
}

Step 3: Submit the transaction

Two options depending on who submits.

Option A: Buyer submits

The buyer submits the transferWithAuthorization transaction directly and pays gas. Use this when the buyer controls when and how the payment is executed, for example when the buyer's accounting system needs the tx hash tied to an internal approval flow.

// pay.ts
import { ethers } from "ethers";
import { provider, USDT0_ADDRESS } from "./config";
 
const buyerWallet = new ethers.Wallet(process.env.BUYER_KEY!, provider);
 
const usdt0 = new ethers.Contract(
  USDT0_ADDRESS,
  [
    "function transferWithAuthorization(address from, address to, uint256 value, uint256 validAfter, uint256 validBefore, bytes32 nonce, uint8 v, bytes32 r, bytes32 s)",
  ],
  buyerWallet,
);
 
async function payInvoice(
  authorization: { from: string; to: string; value: bigint; validAfter: number; validBefore: number; nonce: string },
  signature: string,
) {
  const { v, r, s } = ethers.Signature.from(signature);
 
  const tx = await usdt0.transferWithAuthorization(
    authorization.from,
    authorization.to,
    authorization.value,
    authorization.validAfter,
    authorization.validBefore,
    authorization.nonce,
    v, r, s,
  );
 
  const receipt = await tx.wait(1);
  console.log("Invoice paid, tx:", receipt.hash);
  // The nonce is now consumed; the same invoice cannot be paid twice.
  return { txHash: receipt.hash, blockNumber: receipt.blockNumber };
}

Option B: Vendor submits

The buyer sends {authorization, signature} to the vendor through API, email, or any channel. The vendor (or a facilitator) submits the transaction on the buyer's behalf, so the buyer does not need to manage gas. Use this when the vendor needs synchronous confirmation within the same request flow.

// settle.ts
import { ethers } from "ethers";
import { provider, USDT0_ADDRESS } from "./config";
 
const vendorWallet = new ethers.Wallet(process.env.VENDOR_KEY!, provider);
 
const usdt0 = new ethers.Contract(
  USDT0_ADDRESS,
  [
    "function transferWithAuthorization(address from, address to, uint256 value, uint256 validAfter, uint256 validBefore, bytes32 nonce, uint8 v, bytes32 r, bytes32 s)",
  ],
  vendorWallet,
);
 
async function settleInvoice(
  authorization: { from: string; to: string; value: bigint; validAfter: number; validBefore: number; nonce: string },
  signature: string,
) {
  const { v, r, s } = ethers.Signature.from(signature);
 
  const tx = await usdt0.transferWithAuthorization(
    authorization.from,
    authorization.to,
    authorization.value,
    authorization.validAfter,
    authorization.validBefore,
    authorization.nonce,
    v, r, s,
  );
 
  const receipt = await tx.wait(1);
  console.log("Invoice settled, tx:", receipt.hash);
  return { txHash: receipt.hash, blockNumber: receipt.blockNumber };
}

Step 4: Reconcile via on-chain events (vendor)

Regardless of who submitted the transaction, every invoice payment emits an AuthorizationUsed event carrying the deterministic nonce. The vendor listens for this event and matches it to a pending invoice by nonce. Because the nonce is derived from invoice metadata, matching is exact.

// reconcile.ts
import { ethers } from "ethers";
import { provider, USDT0_ADDRESS, Invoice } from "./config";
import { getInvoiceNonce } from "./nonce";
 
const usdt0 = new ethers.Contract(
  USDT0_ADDRESS,
  [
    "event AuthorizationUsed(address indexed authorizer, bytes32 indexed nonce)",
    "event Transfer(address indexed from, address indexed to, uint256 value)",
  ],
  provider,
);
 
// Build a lookup map: nonce -> invoice.
// In production, this comes from your invoice database.
const invoices: Invoice[] = [
  {
    number: "INV-2026-001234",
    vendor: "0xVendorAddress",
    buyer: "0xBuyerAddress",
    amount: ethers.parseUnits("5000", 6),
    dueDate: Math.floor(new Date("2026-04-30").getTime() / 1000),
  },
];
 
const nonceToInvoice = new Map<string, Invoice>();
for (const inv of invoices) {
  nonceToInvoice.set(getInvoiceNonce(inv), inv);
}
 
usdt0.on("AuthorizationUsed", async (authorizer: string, nonce: string, event: any) => {
  const invoice = nonceToInvoice.get(nonce);
  if (!invoice) return; // not one of our invoices
 
  const receipt = await event.getTransactionReceipt();
 
  const transferLog = receipt.logs
    .map((log: any) => {
      try { return usdt0.interface.parseLog(log); } catch { return null; }
    })
    .find(
      (parsed: any) =>
        parsed?.name === "Transfer" &&
        parsed.args[0].toLowerCase() === invoice.buyer.toLowerCase() &&
        parsed.args[1].toLowerCase() === invoice.vendor.toLowerCase() &&
        parsed.args[2] === invoice.amount
    );
 
  if (!transferLog) {
    console.error("No matching Transfer event for invoice:", invoice.number);
    return;
  }
 
  // All checks passed
  console.log(`Invoice ${invoice.number} PAID`);
  console.log("  tx:", receipt.hash);
  console.log("  settled at block:", receipt.blockNumber);
 
  // In production: update your ERP/accounting system here
  // erpSystem.markPaid(invoice.number, receipt.hash, receipt.blockNumber);
});
 
console.log("Listening for invoice settlements...");

npx tsx reconcile.ts

Listening for invoice settlements...
Invoice INV-2026-001234 PAID
  tx: 0x8f3a...2d41
  settled at block: 1284371

Handle failed payments

A submitted transferWithAuthorization can revert for several reasons. Detect and surface each one to the vendor or buyer so the invoice can be retried or closed.

Revert reason	Cause	Recovery
`FiatTokenV2: invalid signature`	Signature doesn't match the authorization fields.	Ask buyer to re-sign with unchanged invoice data.
`FiatTokenV2: authorization is used or canceled`	Nonce was already consumed (double-submission) or the buyer cancelled it.	Mark the invoice as already-paid; look up the original tx by nonce.
`FiatTokenV2: authorization is not yet valid`	Submitted before `validAfter`.	Wait until `validAfter` or issue a new authorization.
`FiatTokenV2: authorization is expired`	Submitted after `validBefore`.	Issue a new authorization with an extended window.
`FiatTokenV2: transfer amount exceeds balance`	Buyer's USDT0 balance is insufficient.	Notify buyer to fund their wallet, then retry the same signature.

Catch reverts and classify them before retrying.

// retry.ts
import { ethers } from "ethers";
 
async function submitWithRetry(
  submit: () => Promise<ethers.ContractTransactionResponse>,
): Promise<string> {
  try {
    const tx = await submit();
    const receipt = await tx.wait(1);
    return receipt!.hash;
  } catch (err: any) {
    const reason = err?.info?.error?.message || err?.reason || err?.message || "";
 
    if (reason.includes("authorization is used or canceled")) {
      // Lookup the original tx by AuthorizationUsed event; mark invoice paid.
      throw new Error("ALREADY_PAID");
    }
    if (reason.includes("authorization is expired")) {
      throw new Error("AUTHORIZATION_EXPIRED");
    }
    if (reason.includes("invalid signature")) {
      throw new Error("INVALID_SIGNATURE");
    }
    if (reason.includes("transfer amount exceeds balance")) {
      throw new Error("INSUFFICIENT_BALANCE");
    }
    throw err;
  }
}

Next recommended

Invoice settlement concept — Understand the deterministic-nonce reconciliation model.
ERC-3009 — Review the signed-authorization standard behind this flow.
Enable gas-free transactions — Combine with Gas Waiver to eliminate gas from the settlement path.