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AI agents can pay autonomously using EIP-3009 typed data signatures. The agent holds a private key, constructs and signs the TransferWithAuthorization typed data, and calls the settlement endpoint directly. No custodial wallets, no pre-approvals, no subscriptions — the EIP-3009 signature is the authorization.
AI agent payments require the Custom Integration path. The Hosted Gateway requires a browser wallet and is not suitable for agents.

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Agent Payment Flow

1. Agent calls a resource → Server returns 402 with X-Payment-Required header,
   or agent calls POST /api/v1/x402/intents directly to create an intent.

2. Agent reads payment_requirements → picks the chain it has USDC on.

3. Agent generates a random bytes32 nonce and sets validBefore = now + 900.

4. Agent signs TransferWithAuthorization typed data with its private key.

5. Agent calls POST /api/v1/x402/pay with the signature.

6. On success (tx_hash in response), agent proceeds with its original task.
No human interaction is required at any step.

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Minimal Node.js Example (viem)

import { privateKeyToAccount } from "viem/accounts"
import { randomBytes } from "crypto"

const BASE    = "https://testnetv1.ababilpay.xyz"
const account = privateKeyToAccount(process.env.AGENT_PRIVATE_KEY)

async function agentPay(intentId, requirement) {
  // 1. Derive chain ID from CAIP-2 network identifier
  const chainId     = parseInt(requirement.network.split(":")[1])

  // 2. Generate a fresh random nonce — never reuse
  const nonce       = `0x${randomBytes(32).toString("hex")}`

  // 3. Set validBefore to 15 minutes from now
  const validBefore = BigInt(Math.floor(Date.now() / 1000) + 900)

  // 4. Sign TransferWithAuthorization typed data
  const signature = await account.signTypedData({
    domain: {
      name:              requirement.usdcDomainName,  // from API — "USDC"
      version:           "2",
      chainId,
      verifyingContract: requirement.asset,
    },
    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" },
      ],
    },
    primaryType: "TransferWithAuthorization",
    message: {
      from:        account.address,
      to:          requirement.payTo,
      value:       BigInt(requirement.maxAmountRequired),
      validAfter:  0n,
      validBefore,
      nonce,
    },
  })

  // 5. Submit settlement request
  const res = await fetch(`${BASE}/api/v1/x402/pay`, {
    method: "POST",
    headers: {
      "Authorization": `Bearer ${process.env.MERCHANT_API_KEY}`,
      "Content-Type":  "application/json",
    },
    body: JSON.stringify({
      intent_id: intentId,
      payment_signature: {
        scheme:      "exact",
        network:     requirement.network,
        x402Version: 1,
        payload: {
          from:        account.address,
          to:          requirement.payTo,
          value:       requirement.maxAmountRequired,
          validAfter:  "0",
          validBefore: validBefore.toString(),
          nonce,
          signature,
        },
      },
    }),
  })

  return res.json()
  // → { success: true, data: { tx_hash, settled_at, amount_usdc, network } }
}

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End-to-End Agent Example

async function payAndProceed(amountUsdc, task) {
  // Create the payment intent
  const intentRes = await fetch(`${BASE}/api/v1/x402/intents`, {
    method: "POST",
    headers: {
      "Authorization": `Bearer ${process.env.MERCHANT_API_KEY}`,
      "Content-Type":  "application/json",
    },
    body: JSON.stringify({ amount_usdc: amountUsdc }),
  })
  const { data: intent } = await intentRes.json()

  // Pick a requirement — prefer Base Sepolia for speed and low fees
  const requirement =
    intent.payment_requirements.find((r) => r.network === "eip155:84532")
    ?? intent.payment_requirements[0]

  if (!requirement) throw new Error("No supported chain found")

  // Sign and settle
  const result = await agentPay(intent.intent_id, requirement)

  if (!result.success) throw new Error(`Payment failed: ${result.error?.code}`)

  console.log(`Payment settled: ${result.data.tx_hash}`)

  // Proceed with the original task
  return task()
}

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Key Considerations for Agents

Private key security — store the agent’s signing key in an environment variable or secrets manager. Never embed it in code or commit it to version control. Chain selection — query payment_requirements at runtime and select the chain your agent holds USDC on. Do not hardcode chain IDs. Nonce management — generate a fresh crypto.randomBytes(32) for every payment. The EIP-3009 nonce is not a counter; the USDC contract records each nonce permanently to prevent replay attacks. Idempotency — if a settlement call fails with a network error (timeout, 5xx), check the intent status (GET /intents/{id}) before retrying. The intent may have already been marked paid — retrying with the same or a new signature on a paid intent returns ALREADY_PAID. USDC balance — ensure your agent’s wallet holds sufficient testnet USDC before executing payments. Insufficient balance causes SETTLEMENT_FAILED. See the Supported Networks page for testnet USDC contract addresses.