EIP-3009 Signing Reference

signEip3009Authorization builds and signs a real EIP-3009 TransferWithAuthorization payload — ready to send as the eip3009 scheme’s paymentPayload to /verify or /settle, or to hand a merchant directly as an X-PAYMENT header.

This performs a genuine EIP-712 signature. There is no mock mode — signing is pure local cryptography with no network dependency, so it works offline and never touches XentFi’s servers.

Signature

function signEip3009Authorization(
  params: SignExactAuthorizationParams
): Promise<Eip3009SchemePayload>;

Parameters

Parameter	Type	Required	Description
`account`	`LocalAccount`	✅	Any viem local account that implements `signTypedData` — from `privateKeyToAccount`, a hardware wallet adapter, etc.
`to`	`Address`	✅	Recipient address (the merchant’s `payTo`).
`amount`	`string`	✅	Amount in the token’s own human-readable units, e.g. `"2.50"` — converted to base units using `domain.tokenDecimals`.
`domain`	`Eip3009TokenDomain`	✅	The token’s real EIP-712 domain — see below.
`validitySeconds`	`number`	optional	How long the authorization stays valid for, in seconds from now. Default `300` (5 minutes).
`nonce`	`Hex`	optional	Supply your own bytes32 nonce for deterministic/idempotent authorizations; otherwise a random one is generated with `crypto.getRandomValues`.

`Eip3009TokenDomain`

interface Eip3009TokenDomain {
  chainId: number;
  tokenAddress: Address;
  tokenName: string;
  tokenVersion: string;
  tokenDecimals: number;
}

Returns — `Eip3009SchemePayload`

interface Eip3009SchemePayload {
  scheme: "eip3009";
  from: Address;
  to: Address;
  value: string;        // token base units, as a decimal string
  validAfter: string;   // unix seconds
  validBefore: string;  // unix seconds
  nonce: Hex;            // bytes32
  signature: Hex;
}

The underlying EIP-712 type

const TRANSFER_WITH_AUTHORIZATION_TYPES = {
  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" },
  ],
} as const;

buildEip3009Domain(token: Eip3009TokenDomain) builds the matching EIP-712 domain object ({ name, version, chainId, verifyingContract }) if you need to construct or verify a signature manually rather than through signEip3009Authorization.

Example: custom nonce for idempotency

const payload = await signEip3009Authorization({
  account,
  to: "0xMerchantWalletAddress",
  amount: "2.50",
  domain: {
    chainId: 8453,
    tokenAddress: "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    tokenName: "USD Coin",
    tokenVersion: "2",
    tokenDecimals: 6,
  },
  nonce: "0x0000000000000000000000000000000000000000000000000000000000000001",
});

A deterministic nonce (derived from your own request/order ID, for example) lets you safely retry signing the same logical payment without risking a double-spend — the contract rejects a reused nonce for the same signer.

Security notes

validBefore is set from validitySeconds (default 5 minutes) — keep this short. A long-lived signed authorization is a bearer instrument until it either expires or is consumed.
validAfter is always 0 in the current implementation (immediately valid).
The signature never leaves the caller’s process during signing — only the final Eip3009SchemePayload (which includes the signature, not the private key) is transmitted anywhere.

Next steps

Payer Guide

See this used in a full 402 round trip.

API Reference

X402FacilitatorClient and the rest of the type surface.

Getting Started

Guides

Reference

Signature

Parameters

`Eip3009TokenDomain`

Returns — `Eip3009SchemePayload`

The underlying EIP-712 type

Example: custom nonce for idempotency

Security notes

Next steps

Payer Guide

API Reference

​Signature

​Parameters

​Eip3009TokenDomain

​Returns — Eip3009SchemePayload

​The underlying EIP-712 type

​Example: custom nonce for idempotency

​Security notes

​Next steps

Payer Guide

API Reference

Signature

Parameters

`Eip3009TokenDomain`

Returns — `Eip3009SchemePayload`

The underlying EIP-712 type

Example: custom nonce for idempotency

Security notes

Next steps