x402 Quickstart for Sellers

This tutorial shows how to add x402 v2 payment middleware to your API or service. By the end, buyers and AI agents will automatically pay in USDC when accessing your protected endpoints.

Polygon facilitators on Amoy and mainnet run x402 v2. Use the @x402/* packages below. For Go or Python server examples, see the official x402 seller quickstart.

These snippets are for demonstration only. Store private keys and facilitator URLs in a secure vault. Never hardcode secrets.

Prerequisites

Requirement	Example / Notes
Wallet to receive USDC	Any EVM-compatible wallet (Metamask, Rabby, Safe, etc.)
Node.js	Node.js 18+ with npm or Bun
Existing API / server	Express, Next.js, or Hono
Polygon network	Amoy testnet or mainnet

This guide starts with Amoy testnet configuration. See Running on Polygon mainnet when you are ready for production.

Install dependencies

Wherever bun is used, replace it with npm or your preferred package manager.

Express
Next.js
Hono

bun install @x402/express @x402/core @x402/evm express

bun install @x402/next @x402/core @x402/evm

bun install @x402/hono @x402/core @x402/evm hono @hono/node-server

Add payment middleware

Integrate payment middleware with:

A facilitator client pointing at the Polygon Amoy facilitator
An x402ResourceServer with the EVM scheme registered
Route config using an accepts array with scheme, price, network, and payTo

Express
Next.js
Hono

Full example in the x402 repo.

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

const app = express();
const payTo = "0xYourEvmAddress";

const facilitatorClient = new HTTPFacilitatorClient({
  url: process.env.FACILITATOR_URL || "https://x402-amoy.polygon.technology",
});

app.use(
  paymentMiddleware(
    {
      "GET /weather": {
        accepts: [
          {
            scheme: "exact",
            price: "$0.001",
            network: "eip155:80002",
            payTo,
          },
        ],
        description: "Get current weather data for any location",
        mimeType: "application/json",
      },
    },
    new x402ResourceServer(facilitatorClient).register(
      "eip155:80002",
      new ExactEvmScheme()
    )
  )
);

app.get("/weather", (_req, res) => {
  res.send({
    report: { weather: "sunny", temperature: 70 },
  });
});

app.listen(4021, () => {
  console.log("Server running at http://localhost:4021");
});

Full example in the x402 repo.Use withX402 for API routes. It settles payment only after a successful response (status below 400).

// lib/x402-server.ts
import { x402ResourceServer, HTTPFacilitatorClient } from "@x402/core/server";
import { ExactEvmScheme } from "@x402/evm/exact/server";

export const payTo = "0xYourEvmAddress";

const facilitatorClient = new HTTPFacilitatorClient({
  url: process.env.FACILITATOR_URL || "https://x402-amoy.polygon.technology",
});

export const server = new x402ResourceServer(facilitatorClient).register(
  "eip155:80002",
  new ExactEvmScheme()
);

// app/api/weather/route.ts
import { NextRequest, NextResponse } from "next/server";
import { withX402 } from "@x402/next";
import { payTo, server } from "../../../lib/x402-server";

const handler = async (_: NextRequest) => {
  return NextResponse.json(
    {
      report: { weather: "sunny", temperature: 72 },
    },
    { status: 200 }
  );
};

export const GET = withX402(
  handler,
  {
    accepts: [
      {
        scheme: "exact",
        price: "$0.001",
        network: "eip155:80002",
        payTo,
      },
    ],
    description: "Access to weather API",
    mimeType: "application/json",
  },
  server
);

Full example in the x402 repo.

import { Hono } from "hono";
import { serve } from "@hono/node-server";
import { paymentMiddleware, x402ResourceServer } from "@x402/hono";
import { ExactEvmScheme } from "@x402/evm/exact/server";
import { HTTPFacilitatorClient } from "@x402/core/server";

const app = new Hono();
const payTo = "0xYourEvmAddress";

const facilitatorClient = new HTTPFacilitatorClient({
  url: process.env.FACILITATOR_URL || "https://x402-amoy.polygon.technology",
});

app.use(
  paymentMiddleware(
    {
      "GET /weather": {
        accepts: [
          {
            scheme: "exact",
            price: "$0.001",
            network: "eip155:80002",
            payTo,
          },
        ],
        description: "Weather data",
        mimeType: "application/json",
      },
    },
    new x402ResourceServer(facilitatorClient).register(
      "eip155:80002",
      new ExactEvmScheme()
    )
  )
);

app.get("/weather", (c) => {
  return c.json({
    report: { weather: "sunny", temperature: 70 },
  });
});

serve({ fetch: app.fetch, port: 4021 });

Buyers calling protected routes receive a 402 challenge, pay via the facilitator, and then receive the response.

Running on Polygon mainnet

Once you have tested on Amoy, switch to mainnet:

1. Update the facilitator URL

const facilitatorClient = new HTTPFacilitatorClient({
  url: "https://x402.polygon.technology",
});

2. Update the network identifier

Change eip155:80002 (Amoy) to eip155:137 (Polygon mainnet) in every accepts entry and scheme registration:

// Testnet → Mainnet
network: "eip155:137",
// ...
server.register("eip155:137", new ExactEvmScheme());

Both Polygon facilitators run x402 v2. See Using the Polygon Facilitator for signer addresses and health endpoints.

Reference

Schema

name	type	required	example	description
`payTo`	string	yes	`0xYourAddress`	Address that receives USDC
`network`	string	yes	`eip155:80002`	CAIP-2 network ID (Amoy or `eip155:137` for mainnet)
`scheme`	string	yes	`"exact"`	Payment scheme
`price`	string	yes	`"$0.001"`	Cost per request in USDC
`FACILITATOR_URL`	string	optional	`"https://x402-amoy.polygon.technology"`	Polygon facilitator endpoint
`description`	string	optional	`"Weather data"`	Used for discoverability in x402 Bazaar
`mimeType`	string	optional	`"application/json"`	Response content type

Errors

case / code	meaning	fix
`402_LOOP`	Client cannot fulfill payment	Check facilitator URL, network ID, and wallet
`INVALID_NETWORK`	Wrong network identifier	Use `eip155:80002` (Amoy) or `eip155:137` (mainnet)
`BAD_CONFIG`	Missing route config	Define `accepts`, `price`, `network`, and `payTo` per route

Do / Don’t Do Guardrails

Do	Don’t
Use `https://x402-amoy.polygon.technology` for Amoy testing	Use legacy `x402-express` against Polygon facilitators
Use `https://x402.polygon.technology` for mainnet	Expose private keys in middleware
Test on Amoy before mainnet	Use V1 network strings like `"polygon-amoy"` or `"polygon"`
Include `description` and `mimeType` for AI discoverability	Skip `payTo` in route config

Documentation Index

​Prerequisites

​Install dependencies

​Add payment middleware

​Running on Polygon mainnet

​1. Update the facilitator URL

​2. Update the network identifier

​Reference

​Schema

​Errors

​Do / Don’t Do Guardrails

​References

Prerequisites

Install dependencies

Add payment middleware

Running on Polygon mainnet

1. Update the facilitator URL

2. Update the network identifier

Reference

Schema

Errors

Do / Don’t Do Guardrails

References