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Pay for an x402 API with delegation

In this guide, you use a buyer account to access API data from an x402 server by creating a delegationDelegation The ability for a MetaMask smart account to authorize another account to perform specific executions on its behalf. that authorizes token transfers on your behalf.

You use createx402DelegationProvider to set up an x402Erc7710Client with a delegation provider, register it with the x402 client, and use wrapFetchWithPayment to automatically handle payment when calling a protected API route.

Prerequisites​

Steps​

1. Install the dependencies​

npm install @x402/core @x402/fetch @metamask/x402

2. Create a buyer account​

Create an account to represent the buyer, the delegatorDelegator account The account that creates and signs a delegation to grant limited authority to another account. who creates a delegation.

The delegator must be a MetaMask smart accountMetaMask smart account A smart contract account created using the Smart Accounts Kit that supports programmable behavior, flexible signing options, and ERC-7710 delegations.. Use the toolkit's toMetaMaskSmartAccount method to create the buyer account.

Important

Fund the smart account with USDC for the requested payment.

import { Implementation, toMetaMaskSmartAccount } from '@metamask/smart-accounts-kit'
import { publicClient, buyerAccount } from './config'

export const buyerSmartAccount = await toMetaMaskSmartAccount({
  client: publicClient,
  implementation: Implementation.Hybrid,
  deployParams: [buyerAccount.address, [], [], []],
  deploySalt: '0x',
  signer: { account: buyerAccount },
})

3. Create an x402 ERC-7710 client​

Create an x402Erc7710Client using createx402DelegationProvider. The provider creates an openOpen delegation A delegation that leaves the delegate unspecified, allowing any account to redeem it. root delegationRoot delegation The first delegation in a chain, where an account delegates its own authority directly., signs it, and returns an ABI-encoded delegation chain when the x402 client needs to pay for a request.

The provider appends redeemer, allowedTargets, and timestamp caveatsCaveat A restriction attached to a delegation that limits how delegated authority can be used. if not already present.

import { createx402DelegationProvider } from '@metamask/smart-accounts-kit/experimental'
import { x402Erc7710Client } from '@metamask/x402'

const erc7710Client = new x402Erc7710Client({
  delegationProvider: createx402DelegationProvider({
    account: buyerSmartAccount,
  }),
})

4. Register the client​

Register the ERC-7710 client with the x402 core client for all EVM networks. Create an HTTP client and a payment-aware fetch function using wrapFetchWithPayment.

import { x402Client, x402HTTPClient } from '@x402/core/client'
import { wrapFetchWithPayment } from '@x402/fetch'

const coreClient = new x402Client().register('eip155:*', erc7710Client)
const httpClient = new x402HTTPClient(coreClient)

const fetchWithPayment = wrapFetchWithPayment(fetch, httpClient)

5. Make the paid request​

Call the protected endpoint using fetchWithPayment. It handles the x402 payment flow, calling your delegation provider to create an open delegationOpen delegation A delegation that leaves the delegate unspecified, allowing any account to redeem it. when the server returns a 402 response.

const paidResponse = await fetchWithPayment('https://api.example.com/paid-endpoint', {
  method: 'GET',
})
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