How-to: Set up a Permit2 allowance

Usage-based upto payments move USDC through the Permit2 contract, so the buyer’s USDC allowance for Permit2 must cover each payment. There are two ways to grant the allowance:

Onchain approval: one approve transaction grants Permit2 spending power indefinitely. Best when the buyer transacts repeatedly and can hold the gas asset.
Gasless permit: the buyer signs an EIP-2612 permit for each payment, which you, as the seller, attach to the Facilitator Service call. Best when the buyer can’t hold the gas asset or integrates purely offchain, since Circle pays settlement gas when the permit is applied.

Prerequisites

Before you begin, ensure that you’ve:

Installed Node.js v22.6+
Installed viem
Funded the buyer wallet with Arc testnet USDC from the Circle Faucet

Grant Permit2 spending power

Pick the tab for the way you want to grant the allowance.

Onchain approval
Gasless permit

Send one approve from the buyer, with Permit2 as the spender. The example targets Arc testnet.

approve-permit2.ts

import { createWalletClient, http, erc20Abi, maxUint256 } from "viem";
import { privateKeyToAccount } from "viem/accounts";
import { arcTestnet } from "viem/chains";

const buyer = privateKeyToAccount(
  process.env.BUYER_PRIVATE_KEY as `0x${string}`,
);
const client = createWalletClient({
  account: buyer,
  chain: arcTestnet,
  transport: http(),
});

const hash: `0x${string}` = await client.writeContract({
  address: "0x3600000000000000000000000000000000000000", // USDC on Arc testnet
  abi: erc20Abi,
  functionName: "approve",
  args: ["0x000000000022D473030F116dDEE9F6B43aC78BA3", maxUint256], // Permit2
});

Have the buyer sign the permit under the USDC contract’s own EIP-712 domain, not the Permit2 domain. Use the name and version that USDC reports on that network: USDC on Arc and USD Coin on Base and Polygon PoS, with version 2.

sign-permit.ts

import { createPublicClient, http, parseAbi } from "viem";
import { privateKeyToAccount } from "viem/accounts";
import { arcTestnet } from "viem/chains";

const usdc = "0x3600000000000000000000000000000000000000";
const permit2 = "0x000000000022D473030F116dDEE9F6B43aC78BA3";
const buyer = privateKeyToAccount(
  process.env.BUYER_PRIVATE_KEY as `0x${string}`,
);
const publicClient = createPublicClient({
  chain: arcTestnet,
  transport: http(),
});

const nonce: bigint = await publicClient.readContract({
  address: usdc,
  abi: parseAbi(["function nonces(address owner) view returns (uint256)"]),
  functionName: "nonces",
  args: [buyer.address],
});
const deadline: bigint = BigInt(Math.floor(Date.now() / 1000) + 900);
const value: bigint = 5000000n; // must equal the Permit2 maximum

const signature: `0x${string}` = await buyer.signTypedData({
  domain: {
    name: "USDC",
    version: "2",
    chainId: 5042002,
    verifyingContract: usdc,
  },
  types: {
    Permit: [
      { name: "owner", type: "address" },
      { name: "spender", type: "address" },
      { name: "value", type: "uint256" },
      { name: "nonce", type: "uint256" },
      { name: "deadline", type: "uint256" },
    ],
  },
  primaryType: "Permit",
  message: { owner: buyer.address, spender: permit2, value, nonce, deadline },
});

The buyer sends the signature and permit fields to you to attach to each Facilitator Service call.

If a permit is present but invalid, Facilitator Service returns one of the permit reasons on /verify or /settle.

Circle CLI

Agent marketplace

x402 facilitators

How-to: Set up a Permit2 allowance

Prerequisites

Grant Permit2 spending power

​Prerequisites

​Grant Permit2 spending power

Prerequisites

Grant Permit2 spending power