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Express.js

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Install

npm install @x402/express @x402/evm @x402/core
For Solana support, also install @x402/svm: 
npm install @x402/svm

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Minimal example (EVM)

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 facilitatorClient = new HTTPFacilitatorClient({
  url: process.env.FACILITATOR_URL!,
});

app.use(
  paymentMiddleware(
    {
      "GET /weather": {
        accepts: [
          {
            scheme: "exact",
            price: "$0.10",
            network: "eip155:8453",           // Base mainnet
            payTo: process.env.EVM_ADDRESS!,  // your wallet
          },
        ],
        description: "Weather data",
        mimeType: "application/json",
      },
    },
    new x402ResourceServer(facilitatorClient)
      .register("eip155:8453", new ExactEvmScheme()),
  ),
);

app.get("/weather", (req, res) => {
  res.json({ weather: "sunny", temperature: 70 });
});

app.listen(4021);

​
Minimal example (Solana)

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

const app = express();

const facilitatorClient = new HTTPFacilitatorClient({
  url: process.env.FACILITATOR_URL!,
});

app.use(
  paymentMiddleware(
    {
      "GET /weather": {
        accepts: [
          {
            scheme: "exact",
            price: "$0.10",
            network: "solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp",  // Solana mainnet
            payTo: process.env.SOLANA_ADDRESS!,                    // your wallet
          },
        ],
        description: "Weather data",
        mimeType: "application/json",
      },
    },
    new x402ResourceServer(facilitatorClient)
      .register("solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp", new ExactSvmScheme()),
  ),
);

app.get("/weather", (req, res) => {
  res.json({ weather: "sunny", temperature: 70 });
});

app.listen(4021);

​
Configuration

The paymentMiddleware takes a route map and a resource server: 
paymentMiddleware(routes, resourceServer)
Routes map "METHOD /path" to payment requirements: 
{
  "GET /endpoint": {
    accepts: [{
      scheme: "exact",            // payment scheme
      price: "$0.10",             // human-readable price
      network: "eip155:8453",     // CAIP-2 network ID
      payTo: "0x...",             // your receiving address
    }],
    description: "Endpoint description",
    mimeType: "application/json",
  }
}
Network identifiers use CAIP-2 format:
  • eip155:8453 — Base mainnet
  • eip155:84532 — Base Sepolia (testnet)
  • solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp — Solana mainnet
  • solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1 — Solana Devnet

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Facilitator URL

EnvironmentURL
Sandbox (free, testnet)https://x402.renvoy.ai/sandbox
Production (API key)https://x402.renvoy.ai/v1/YOUR_API_KEY

​
Any framework

If you’re not using Express, you can implement the 402 flow directly. The protocol is framework-agnostic.

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What your server does

  1. Check for payment: Look for the X-PAYMENT header on incoming requests
  2. No payment? Return 402 with payment requirements in the response body
  3. Has payment? Forward it to the facilitator’s /settle endpoint for on-chain settlement
  4. Settlement succeeds? Return the requested resource

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402 response format

When a request arrives without payment, respond with: 
HTTP/1.1 402 Payment Required
Content-Type: application/json

{
  "x402Version": 1,
  "accepts": [
    {
      "scheme": "exact",
      "network": "eip155:8453",
      "maxAmountRequired": "100000",
      "resource": "https://api.example.com/data",
      "description": "API access",
      "mimeType": "application/json",
      "payTo": "0xYourAddress",
      "maxTimeoutSeconds": 60,
      "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
      "extra": {
        "name": "USD Coin",
        "version": "2"
      }
    }
  ]
}
maxAmountRequired is in USDC atomic units (6 decimals). "100000" = 0.10 USDC.

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Settle request

Forward the client’s X-PAYMENT header to the facilitator: 
POST https://x402.renvoy.ai/v1/YOUR_API_KEY/settle
Content-Type: application/json

{
  "paymentPayload": "<base64-encoded payment from X-PAYMENT header>",
  "paymentRequirements": {
    "scheme": "exact",
    "network": "eip155:8453",
    "maxAmountRequired": "100000",
    "resource": "https://api.example.com/data",
    "payTo": "0xYourAddress",
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "extra": { "name": "USD Coin", "version": "2" }
  }
}

​
Settle response

{
  "success": true,
  "transaction": "0xabc123...",
  "network": "eip155:8453",
  "payer": "0xClientAddress"
}