Wire Format

PaymentRequirements (402 Response)

Server sends this to request payment:

{
  "x402Version": 2,
  "accepts": [{
    "scheme": "auth-capture",
    "network": "eip155:8453",
    "amount": "1000000",
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "payTo": "0xReceiverAddress",
    "maxTimeoutSeconds": 60,
    "extra": {
      "name": "USDC",
      "version": "2",
      "captureAuthorizer": "0xCaptureAuthorizerAddress",
      "captureDeadline": 1740758554,
      "refundDeadline": 1741276954,
      "minFeeBps": 0,
      "maxFeeBps": 1000,
      "feeRecipient": "0xFeeRecipientAddress",
      "autoCapture": false,
      "assetTransferMethod": "eip3009"
    }
  }]
}

A server MAY list more than one accepts[] entry with different assetTransferMethod values so clients can pick the method matching their token approvals.

Signing the payload (client)

Clients do not hand-build these payloads. The client half of the scheme ships in the x402 monorepo as AuthCaptureEvmScheme on the @x402/evm/auth-capture/client subpath. Register it on an x402Client and it reads the extra fields, reconstructs the PaymentInfo struct, derives the payer-agnostic nonce, and emits the ERC-3009 (default) or Permit2 payload shown below.

import { AuthCaptureEvmScheme } from '@x402/evm/auth-capture/client'
import { x402Client, wrapFetchWithPayment } from '@x402/fetch'
import { privateKeyToAccount } from 'viem/accounts'

const account = privateKeyToAccount(process.env.EVM_PRIVATE_KEY as `0x${string}`)

const client = new x402Client()
client.register('eip155:*', new AuthCaptureEvmScheme(account))

// fetchWithPayment auto-signs any auth-capture 402 it receives
const fetchWithPayment = wrapFetchWithPayment(fetch, client)

The signer only needs address and signTypedData, so a bare viem LocalAccount works with no PublicClient. The scheme selects ERC-3009 or Permit2 from extra.assetTransferMethod.

PaymentPayload: EIP-3009 (default)

Client sends this with a signed ERC-3009 authorization:

{
  "x402Version": 2,
  "resource": {
    "url": "https://api.example.com/resource",
    "method": "GET"
  },
  "accepted": {
    "scheme": "auth-capture",
    "network": "eip155:8453",
    "amount": "1000000",
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "payTo": "0xReceiverAddress",
    "maxTimeoutSeconds": 60,
    "extra": { "..." }
  },
  "payload": {
    "authorization": {
      "from": "0xPayerAddress",
      "to": "0xEIP3009TokenCollectorAddress",
      "value": "1000000",
      "validAfter": "0",
      "validBefore": "1740675754",
      "nonce": "0xf374...3480"
    },
    "signature": "0x2d6a...571c",
    "salt": "0x0000000000000000000000000000000000000000000000000000000000000abc"
  }
}

PaymentPayload: Permit2

When extra.assetTransferMethod === "permit2", the client signs a Permit2 PermitTransferFrom:

{
  "x402Version": 2,
  "resource": { "url": "https://api.example.com/resource", "method": "GET" },
  "accepted": { "scheme": "auth-capture", "...": "..." },
  "payload": {
    "permit2Authorization": {
      "from": "0xPayerAddress",
      "permitted": {
        "token": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
        "amount": "1000000"
      },
      "spender": "0xPermit2TokenCollectorAddress",
      "nonce": "11021048692073456...",
      "deadline": "1740675754"
    },
    "signature": "0x2d6a...571c",
    "salt": "0x0000000000000000000000000000000000000000000000000000000000000abc"
  }
}

The deterministic nonce binds the merchant address (no witness struct).

Field Reference

Required Extra Fields

Field	Type	Description
`name`	string	EIP-712 token-domain name (for example, `"USDC"`). Used for ERC-3009 signing only.
`version`	string	EIP-712 token-domain version (for example, `"2"`).
`captureAuthorizer`	address	Address that may call `authorize`, `capture`, `void`, `refund`, or `charge`. Committed on-chain as `PaymentInfo.operator`.
`captureDeadline`	uint48	Absolute Unix seconds: capture must occur before this. Encoded as `authorizationExpiry`.
`refundDeadline`	uint48	Absolute Unix seconds: refunds allowed until this. Encoded as `refundExpiry`.
`feeRecipient`	address	Fee recipient. Set to `address(0)` to let the captureAuthorizer specify any non-zero recipient at capture/charge time.
`minFeeBps`	uint16	Lowest fee in basis points the captureAuthorizer must take. `0` = no floor.
`maxFeeBps`	uint16	Highest fee in basis points the captureAuthorizer can take.

Optional Extra Fields

Field	Type	Description	Default
`autoCapture`	`bool`	`true` → facilitator calls `charge()` (atomic). `false` → `authorize()` (two-phase).	`false`
`assetTransferMethod`	`"eip3009"` \| `"permit2"`	Which token collector to use.	`"eip3009"`

Fee Configuration: The escrow enforces fees on-chain via the PaymentInfo struct. The escrow rejects captures/charges that fall outside [minFeeBps, maxFeeBps]. If feeRecipient is non-zero, the actual fee recipient at capture/charge must match.

Nonce Derivation

The signature nonce is the payer-agnostic PaymentInfo hash. The encoding zeros out the payer; every other field carries the value that will appear on-chain.

paymentInfoHash = keccak256(abi.encode(PAYMENT_INFO_TYPEHASH, paymentInfoWithZeroPayer))
nonce           = keccak256(abi.encode(chainId, AUTH_CAPTURE_ESCROW_ADDRESS, paymentInfoHash))

The salt field enforces freshness: each signing call generates a fresh bytes32 salt, so two payers signing concurrently produce distinct nonces with no collision risk.

PaymentRequirements (402 Response)

Signing the payload (client)

PaymentPayload: EIP-3009 (default)

PaymentPayload: Permit2

Field Reference

Required Extra Fields

Optional Extra Fields

Nonce Derivation

Next Steps

Verification and Settlement

PaymentInfo Struct

​PaymentRequirements (402 Response)

​Signing the payload (client)

​PaymentPayload: EIP-3009 (default)

​PaymentPayload: Permit2

​Field Reference

​Required Extra Fields

​Optional Extra Fields

​Nonce Derivation

​Next Steps

Verification and Settlement

PaymentInfo Struct

PaymentRequirements (402 Response)

Signing the payload (client)

PaymentPayload: EIP-3009 (default)

PaymentPayload: Permit2

Field Reference

Required Extra Fields

Optional Extra Fields

Nonce Derivation

Next Steps