Inference an agent can buy by itself.

import { x402Client, x402HTTPClient } from "@x402/core/client";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

const URL = "https://ai.dagentx.com/v1/chat/completions";
const agent = privateKeyToAccount(process.env.AGENT_KEY);   // holds USDC on Monad
const x402 = new x402Client();
x402.setSpendControls({ maxAmountPerPayment: "$1" });      // never pay more than this per call
registerExactEvmScheme(x402, { signer: agent, networks: ["eip155:143"] });
const http = new x402HTTPClient(x402);

const body = JSON.stringify({ model: "venice/zai-org-glm-5", max_tokens: 400,
  messages: [{ role: "user", content: "Summarize x402 in one line" }] });
const init = { method: "POST", headers: { "content-type": "application/json" }, body };

let res = await fetch(URL, init);
if (res.status === 402) {
  const required = http.getPaymentRequiredResponse((h) => res.headers.get(h), await res.json());
  const payment = await http.createPaymentPayload(required);
  res = await fetch(URL, { ...init, headers: { ...init.headers, ...http.encodePaymentSignatureHeader(payment) } });
}
console.log((await res.json()).choices[0].message.content);

import { createSiweMessage } from "viem/siwe";
import { randomBytes } from "node:crypto";

// 1. once: POST https://ai.dagentx.com/v1/x402/top-up?usd=10 and pay the 402 (same as per call)

// 2. every call: a fresh, single-use sign-in for that exact URL
async function signIn(agent, url) {
  const now = new Date();
  const message = createSiweMessage({
    domain: "ai.dagentx.com", uri: url, chainId: 143, version: "1",
    address: agent.address, statement: "Sign in to WRAITH Nexus",
    nonce: randomBytes(12).toString("hex"),
    issuedAt: now, expirationTime: new Date(now.getTime() + 5 * 60_000),
  });
  const signature = await agent.signMessage({ message });
  return Buffer.from(JSON.stringify({ address: agent.address, message, signature, chainId: 143 })).toString("base64");
}

const url = "https://ai.dagentx.com/v1/chat/completions";
const res = await fetch(url, { method: "POST", body,
  headers: { "content-type": "application/json", "SIGN-IN-WITH-X": await signIn(agent, url) } });

// balance and usage: GET /relay/account with a sign-in for that URL

→ POST /v1/chat/completions            (no Authorization header)
← 402  PAYMENT-REQUIRED: base64(JSON)
       { "x402Version": 2,
         "resource": { "url": "https://ai.dagentx.com/v1/chat/completions", … },
         "accepts": [{ "scheme": "exact", "network": "eip155:143",
                       "asset": "0x754704Bc059F8C67012fEd69BC8A327a5aafb603",   // USDC
                       "amount": "8400",                                         // $0.0084, 6 decimals
                       "payTo": "<relay wallet>", "maxTimeoutSeconds": 300,
                       "extra": { "name": "USDC", "version": "2" } }] }

   Sign an EIP-3009 transferWithAuthorization for exactly those terms.

→ POST /v1/chat/completions
  PAYMENT-SIGNATURE: base64({ x402Version: 2, accepted: <the offer>, payload: { signature, authorization } })
← 200  PAYMENT-RESPONSE: base64({ success, transaction, network, payer })

SIGN-IN-WITH-X = base64({ address, message, signature, chainId: 143 })
  message: EIP-4361 (SIWE), domain ai.dagentx.com, uri = the exact URL called,
  chain id 143, issued ≤ 5 minutes ago, nonce used once.