EVM Scheme (USDC on Base)

The EVM scheme uses USDC on Base with EIP-3009 TransferWithAuthorization for gasless, signature-based payments.

Network Parameters

Parameter	Value
Network	base (Chain ID: 8453)
Currency	USDC
Asset (contract)	0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913
Decimals	6 (1000000 = 1.0 USDC)
Token name	USD Coin
Token version	2
CAIP-2	eip155:8453
Testnet	base-sepolia (Chain ID: 84532, USDC: 0x036CbD53842c5426634e7929541eC2318f3dCF7e)

402 Response Example

When a server requires EVM payment, it returns:

{
  "x402Version": 1,
  "accepts": [
    {
      "x402Version": 1,
      "scheme": "exact",
      "network": "base",
      "maxAmountRequired": "10000",
      "resource": "/api/data",
      "description": "API access fee",
      "payTo": "0xRecipientAddress...",
      "maxTimeoutSeconds": 60,
      "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
      "extra": {
        "name": "USD Coin",
        "version": "2"
      }
    }
  ]
}

X-Payment Payload

The client constructs and base64-encodes the following JSON as the X-Payment header:

{
  "x402Version": 1,
  "scheme": "exact",
  "network": "base",
  "payload": {
    "signature": "0x...",
    "authorization": {
      "from": "0xPayerWallet...",
      "to": "0xRecipientAddress...",
      "value": "10000",
      "validAfter": "1700000000",
      "validBefore": "1700000060",
      "nonce": "0x<32-byte-random-hex>"
    }
  }
}

Payload Fields

Field	Type	Description
signature	0x{string}	EIP-712 signature over the authorization
authorization.from	address	Payer's wallet address
authorization.to	address	Recipient address (payTo from 402 response)
authorization.value	uint256	Amount in USDC atomic units (6 decimals)
authorization.validAfter	uint256	Unix timestamp — signature valid after this time
authorization.validBefore	uint256	Unix timestamp — signature expires at this time
authorization.nonce	bytes32	Random 32-byte nonce (0x + 64 hex chars)

Validity Window

• Default: 60 seconds
• Minimum: 30 seconds
• Maximum: configurable (default 300 seconds)
• validAfter = now - 1, validBefore = now + windowSeconds

EIP-712 Type Definition

The signature uses the USDC EIP-3009 TransferWithAuthorization typed data:

{
  "domain": {
    "name": "USD Coin",
    "version": "2",
    "chainId": 8453,
    "verifyingContract": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913"
  },
  "primaryType": "TransferWithAuthorization",
  "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" }
    ]
  }
}

Verification

The facilitator recovers the signer from the EIP-712 signature and verifies:

1. Recovered address matches authorization.from
2. authorization.to matches the expected recipient
3. authorization.value matches the required amount
4. Current time is within validAfter / validBefore window
5. Nonce has not been used

Settlement

Settlement executes an on-chain USDC transferWithAuthorization call on Base using the signed authorization. The facilitator submits the transaction and returns the on-chain txHash.

After settlement, the server includes the transaction hash in the X-Payment-Response header:

{
  "success": true,
  "transaction": "0x..."
}