Minimal TypeScript seller pattern

SameDayDesk's public gateway uses the official x402 TypeScript packages with an Express server. The reduced pattern below shows the same component boundaries without copying product-specific routes or credentials.

import express from "express";
import { paymentMiddleware } from "@x402/express";
import { x402ResourceServer, HTTPFacilitatorClient } from "@x402/core/server";
import { ExactEvmScheme } from "@x402/evm/exact/server";

const app = express();
const network = "eip155:8453";

const facilitator = new HTTPFacilitatorClient({
  url: process.env.X402_FACILITATOR_URL,
});

const resourceServer = new x402ResourceServer(facilitator).register(
  network,
  new ExactEvmScheme(),
);

app.use(
  paymentMiddleware(
    {
      "GET /paid": {
        accepts: {
          scheme: "exact",
          network,
          payTo: process.env.X402_PAY_TO,
          price: "$0.01",
        },
        description: "Example paid resource",
        mimeType: "application/json",
      },
    },
    resourceServer,
  ),
);

app.get("/paid", (_req, res) => {
  res.json({ ok: true });
});

Production requirements

The snippet is intentionally small. A real seller should also add:

• Startup validation for the facilitator URL, payment receiver, network, and asset.
• Request limits and timeouts before any expensive work begins.
• Idempotency around work that must not repeat after a paid retry.
• Structured logs that keep payment identifiers while excluding signatures and secrets.
• A public /.well-known/x402 resource manifest for agent discovery.
• Tests for the unpaid 402 response, paid retry, failed verification, and settlement result.

For the complete public implementation, see the SameDayDesk gateway repository. For SDK behavior and current signatures, use the upstream x402 repository and the generated API reference in this site.