x402: Add Celo to your endpoint

// Base (8453) and Celo mainnet (42220). Node 20+. npm i express @x402/express @x402/core @x402/evm
import express from "express";
import { paymentMiddleware, x402ResourceServer } from "@x402/express";
import { HTTPFacilitatorClient, type RoutesConfig } from "@x402/core/server";
import { ExactEvmScheme } from "@x402/evm/exact/server";

const payTo = "0xYourSellerPayoutAddress"; // example

// Stands in for the facilitator client you already have. Reuse that client
// as configured: building a new one from its URL drops any createAuthHeaders.
const existingFacilitator = new HTTPFacilitatorClient({ url: process.env.FACILITATOR_URL! });

// Celo's hosted facilitator. Note the api. subdomain
const celoFacilitator = new HTTPFacilitatorClient({
  url: "https://api.x402.celo.org",
  createAuthHeaders: async () => {
    const h = { "X-API-Key": process.env.X402_API_KEY! };
    return { verify: h, settle: h, supported: h };
  },
});

// Celo first: for each network the server uses the first facilitator that supports it
const server = new x402ResourceServer([celoFacilitator, existingFacilitator])
  .register("eip155:8453", new ExactEvmScheme())
  .register("eip155:42220", new ExactEvmScheme());

// A Celo mainnet offer for $0.01 in a 6-decimal token
const onCelo = (asset: string, name: string, version: string) => ({
  scheme: "exact",
  network: "eip155:42220" as const,
  payTo,
  price: { amount: "10000", asset, extra: { name, version } },
});

const routes: RoutesConfig = {
  "GET /rates": {
    accepts: [
      { scheme: "exact", network: "eip155:8453", payTo, price: "$0.01" },
      onCelo("0xcebA9300f2b948710d2653dD7B07f33A8B32118C", "USDC", "2"), // Celo mainnet USDC, 6 decimals
      onCelo("0x48065fbBE25f71C9282ddf5e1cD6D6A887483D5e", "Tether USD", "1"), // Celo mainnet USDT, 6 decimals
      onCelo("0xD2ab3C9A02DBBAB236BfEC45D1d755DF4267F771", "Tether America USD", "1"), // Celo mainnet USA₮, 6 decimals
    ],
    description: "Latest FX rates",
    mimeType: "application/json",
  },
};

const app = express();
app.use(paymentMiddleware(routes, server));
app.get("/rates", (_req, res) => res.json({ usd_ngn: 1500 }));
app.listen(3000);

npx @celo/buy quote http://localhost:3000/rates --token USAT

402 Payment Required — http://localhost:3000/rates  (x402 v2, 3 offers)

  3. 0.01 USAT  (10000 atomic)  on celo
     pay to       0xYourSellerPayoutAddress
     payable      yes — matches --token USAT on celo

Nothing was signed or paid. To pay: buy curl with the same arguments.

// Replaces the /rates handler above. Runs behind paymentMiddleware, so the
// buyer's payment is already verified.
app.get("/rates", async (_req, res) => {
  const upstream = await fetch(process.env.UPSTREAM_URL!, {
    headers: { Authorization: `Bearer ${process.env.UPSTREAM_API_KEY}` },
  });
  if (!upstream.ok) {
    res.status(502).json({ error: "upstream_unavailable" });
    return;
  }
  res.json(await upstream.json());
});