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Agents pay for themselves with x402

An agent can fund its own account without a browser, a card, or a human: request a funding order, pay the returned x402 requirements in USDC on Base, and the credit lands on the same balance cards use. Settlement runs through the Coinbase x402 facilitator and is recorded as a Stripe payment. This exact flow is live and proven end to end.

The 20-line client (JavaScript)

// pay.mjs — an agent funding its own AGNT Mail account (this exact flow is proven live)
// npm i @x402/fetch @x402/evm @x402/core viem
import { privateKeyToAccount } from 'viem/accounts';
import { x402Client } from '@x402/core/client';
import { registerExactEvmScheme } from '@x402/evm/exact/client';
import { wrapFetchWithPayment } from '@x402/fetch';

const auth = { Authorization: 'Bearer ' + process.env.MAIL_SECRET, 'Content-Type': 'application/json' };
const wallet = privateKeyToAccount(process.env.WALLET_PRIVATE_KEY);   // holds USDC on Base; no ETH needed

// 1. Create a funding order → HTTP 402 with x402 requirements
const created = await fetch('https://mail.agnt.gg/mail/v1/funding/x402', { method: 'POST', headers: auth, body: JSON.stringify({ amountCents: 1000 }) });
const order = await created.json();                                     // { orderId, state: 'awaiting_payment', requirements }

// 2. Let the x402 client sign and pay. The default spend cap is $1 — raise it or every order is refused.
const client = new x402Client().setSpendControls({ maxAmountPerPayment: '$50' });
registerExactEvmScheme(client, { signer: wallet, networks: ['eip155:8453'] });
const paidFetch = wrapFetchWithPayment(fetch, client);
const paid = await paidFetch('https://mail.agnt.gg/mail/v1/funding/x402/' + order.orderId, { method: 'POST', headers: auth, body: '{}' });
const result = await paid.json();                                       // { state: 'credited', transactionId: '0x…', paymentIntent: 'pi_…' }

// 3. Spend the credit: buy a plan, make an inbox, send mail
await fetch('https://mail.agnt.gg/mail/v1/hosting/purchase', { method: 'POST', headers: { ...auth, 'Idempotency-Key': order.orderId }, body: JSON.stringify({ plan: 'starter' }) });
await fetch('https://mail.agnt.gg/mail/v1/inboxes', { method: 'POST', headers: auth, body: JSON.stringify({ name: 'my-agent' }) });

Two things that will bite you

• Spend cap. @x402/fetch refuses any payment over $1 by default. Every Mail order is $10 or more, so call setSpendControls({ maxAmountPerPayment: '$50' }) or the payment silently fails with a confusing error.
• Your wallet needs USDC on Base and nothing else. The facilitator pays the gas, so you do not need ETH. Easiest way to fund it: Coinbase app → Send → USDC → network Base.

Under the hood (any language)

# Any language. 1) Create the order:
curl -X POST https://mail.agnt.gg/mail/v1/funding/x402 \
  -H 'Authorization: Bearer mail_…' -H 'Content-Type: application/json' -d '{"amountCents":1000}'
# → 402. Body: { orderId, state:"awaiting_payment", expiresAt, requirements }
#   requirements.accepts[0] = { scheme:"exact", network:"eip155:8453", amount:"10000000",
#     asset:"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",   # USDC on Base, 6 decimals
#     payTo:"0x78f1cc529d1de14de8c4b569c25308beb2de87d3", maxTimeoutSeconds:600,
#     extra:{ name:"USD Coin", version:"2" } }             # EIP-712 domain for the signature

# 2) Sign an EIP-3009 transferWithAuthorization for exactly payTo/amount/asset on chain 8453,
#    wrap it in an x402 v2 payment payload, base64 it, and POST it back:
curl -X POST https://mail.agnt.gg/mail/v1/funding/x402/ORDER_ID \
  -H 'Authorization: Bearer mail_…' -H 'PAYMENT-SIGNATURE: <base64 payload>'
# → 200 { state:"credited", transactionId:"0x…", paymentIntent:"pi_…" }  + PAYMENT-RESPONSE header
# → 400 { error, reason, detail } if the wallet lacks USDC, the amount/destination is wrong, or it expired

# 3) Status any time (402 while awaiting, 200 once credited or expired). Retry the SAME order after a timeout.
curl https://mail.agnt.gg/mail/v1/funding/x402/ORDER_ID -H 'Authorization: Bearer mail_…'

Amounts: 1000, 2500 or 5000 cents. Orders expire after 10 minutes; a settled transaction can never be replayed onto another order, and a wrong amount, destination or expired authorization returns 400 without charging. The agent key from headless signup already has the scope this needs. Network eip155:8453 (Base), asset USDC, protocol x402 v2. Compatible with @x402/fetch, Stripe purl, and any v2 client. Card and wallet Checkout remain available for humans.

Automatic email notifications

In your account, open Automatic notifications and register a public HTTPS endpoint. We send signed delivery.accepted, delivery.failed and message.received events. Recipient-server acceptance does not prove inbox placement. Received events identify the inbox; fetch messages with your authorized API key.

GET /mail/v1/webhooks
POST /mail/v1/webhooks {"url":"https://your-app.example/events"}
DELETE /mail/v1/webhooks/ENDPOINT_ID
GET /mail/v1/notifications?after=0
GET /mail/v1/webhook-deliveries
POST /mail/v1/webhook-replay {"eventId":"EVENT_ID","endpointId":"ENDPOINT_ID"}

Owner authentication required. Save the signing secret returned on creation. Verify HMAC-SHA256 over the timestamp, a period, and the exact raw JSON body. Headers: X-AGNT-Timestamp, X-AGNT-Signature (v1=hex), X-AGNT-Event-ID. Reject stale timestamps and deduplicate event IDs. Delivery is at least once, with up to 12 attempts and bounded backoff. Public HTTPS/IPv4 endpoints on port 443 are supported; redirects and private networks are rejected.