Machine-payable rat report

// npm i @solana/web3.js
import { Connection, PublicKey, SystemProgram, Transaction, LAMPORTS_PER_SOL } from "@solana/web3.js";

const ENDPOINT = "https://promptrat.fun/api/x402/rat-report";
const connection = new Connection("https://api.mainnet-beta.solana.com", "confirmed");

// 1. ask for the price - no key, no signup, no account
const challengeRes = await fetch(ENDPOINT);
const challenge = JSON.parse(Buffer.from(challengeRes.headers.get("PAYMENT-REQUIRED"), "base64").toString());
const offer = challenge.accepts.find((o) => o.asset === "So11111111111111111111111111111111111111112");

// 2. pay it yourself: your wallet, your signature, the server never signs anything
const tx = new Transaction().add(SystemProgram.transfer({
  fromPubkey: payer.publicKey,
  toPubkey: new PublicKey(offer.payTo),
  lamports: Number(offer.amount),
}));
tx.feePayer = payer.publicKey;
tx.recentBlockhash = (await connection.getLatestBlockhash()).blockhash;
tx.sign(payer);
const signature = await connection.sendRawTransaction(tx.serialize());
await connection.confirmTransaction(signature, "confirmed");

// 3. retry with the settled signature - the server re-reads it from the chain
const payload = Buffer.from(JSON.stringify({
  x402Version: 2,
  accepted: offer,
  payload: { signature },
})).toString("base64");

const paid = await fetch(ENDPOINT, { headers: { "PAYMENT-SIGNATURE": payload } });
const report = await paid.json();          // 200 + PAYMENT-RESPONSE header
console.log(report.payment, report.stats);