Quickstart for Sellers

Note: This quickstart begins with testnet configuration for safe testing. When you’re ready for production, see Running on Mainnet for the simple changes needed to accept real payments on Base (EVM) and Solana networks.

Prerequisites

Before you begin, ensure you have:

A crypto wallet to receive funds (any EVM or SVM compatible wallet)
Node.js and npm, Go, or Python and pip installed
An existing API or server

Note
There are pre-configured examples available in the x402 repo for both Node.js and Go. There is also an advanced example that shows how to use the x402 SDKs to build a more complex payment flow.

1. Install Dependencies

Install the x402 Express middleware package.

npm install @x402/express @x402/core @x402/evm @x402/svm @x402/avm

Install the x402 Next.js middleware package.

npm install @x402/next @x402/core @x402/evm @x402/svm @x402/avm

Install the x402 Hono middleware package.

npm install @x402/hono @x402/core @x402/evm @x402/svm @x402/avm

Install the x402 Fastify middleware package.

npm install @x402/fastify @x402/core @x402/evm @x402/svm @x402/avm

Add the x402 Go module to your project:

go get github.com/x402-foundation/x402/go

Add the x402 Go module to your project:

go get github.com/x402-foundation/x402/go

Install the x402 Python package with FastAPI support:

pip install "x402[fastapi]"

# For Solana support, also add:
pip install "x402[svm]"

Install the x402 Python package with Flask support:

pip install "x402[flask]"

# For Solana support, also add:
pip install "x402[svm]"

2. Add Payment Middleware

Integrate the payment middleware into your application. You will need to provide:

The Facilitator URL or facilitator client. For testing, use https://x402.org/facilitator which works on Base Sepolia and Solana devnet.
- For mainnet setup, see Running on Mainnet
The routes you want to protect.
Your receiving wallet address.

Full example in the repo here.

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

const app = express();

// Your receiving wallet addresses
const evmAddress = "0xYourEvmAddress";
const svmAddress = "YourSolanaAddress";
const avmAddress = "YourAlgorandAddress";

// Create facilitator client (testnet)
const facilitatorClient = new HTTPFacilitatorClient({
  url: "https://x402.org/facilitator"
});

app.use(
  paymentMiddleware(
    {
      "GET /weather": {
        accepts: [
          {
            scheme: "exact",
            price: "$0.001",
            network: "eip155:84532", // Base Sepolia
            payTo: evmAddress,
          },
          {
            scheme: "exact",
            price: "$0.001",
            network: "solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1", // Solana Devnet
            payTo: svmAddress,
          },
          {
            scheme: "exact",
            price: "$0.001",
            network: "algorand:SGO1GKSzyE7IEPItTxCByw9x8FmnrCDexi9/cOUJOiI=", // Algorand Testnet
            payTo: avmAddress,
          },
        ],
        description: "Weather data",
        mimeType: "application/json",
      },
    },
    new x402ResourceServer(facilitatorClient)
      .register("eip155:84532", new ExactEvmScheme())
      .register("solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1", new ExactSvmScheme())
      .register("algorand:SGO1GKSzyE7IEPItTxCByw9x8FmnrCDexi9/cOUJOiI=", new ExactAvmScheme()),
  ),
);

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

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

Full example in the repo here.Next.js offers two approaches: paymentProxy for protecting page routes (or multiple routes at once), and withX402 for wrapping individual API route handlers. The key difference is that withX402 only settles payment after a successful response (status < 400), making it the recommended approach for API routes.Option A: paymentProxy — best for page routes or protecting multiple routes with a single config:

// proxy.ts
import { paymentProxy } from "@x402/next";
import { x402ResourceServer, HTTPFacilitatorClient } from "@x402/core/server";
import { ExactEvmScheme } from "@x402/evm/exact/server";
import { ExactSvmScheme } from "@x402/svm/exact/server";

export const evmAddress = "0xYourEvmAddress";
export const svmAddress = "YourSolanaAddress";

const facilitatorClient = new HTTPFacilitatorClient({
  url: "https://x402.org/facilitator"
});

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

export const proxy = paymentProxy(
  {
    "/protected": {
      accepts: [
        {
          scheme: "exact",
          price: "$0.001",
          network: "eip155:84532", // Base Sepolia
          payTo: evmAddress,
        },
        {
          scheme: "exact",
          price: "$0.001",
          network: "solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1", // Solana Devnet
          payTo: svmAddress,
        },
      ],
      description: "Premium content",
      mimeType: "text/html",
    },
  },
  server,
);

export const config = {
  matcher: ["/protected/:path*"],
};

Option B: withX402 — recommended for API routes, settles payment only after a successful response:

// app/api/weather/route.ts
import { NextRequest, NextResponse } from "next/server";
import { withX402 } from "@x402/next";
import { server, evmAddress, svmAddress } from "../../../proxy";

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: "eip155:84532", // Base Sepolia
        payTo: evmAddress,
      },
      {
        scheme: "exact",
        price: "$0.001",
        network: "solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1", // Solana Devnet
        payTo: svmAddress,
      },
    ],
    description: "Access to weather API",
    mimeType: "application/json",
  },
  server,
);

Full example in the repo here.

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

const app = new Hono();
const evmAddress = "0xYourEvmAddress";
const svmAddress = "YourSolanaAddress";

const facilitatorClient = new HTTPFacilitatorClient({
  url: "https://x402.org/facilitator"
});

app.use(
  paymentMiddleware(
    {
      "GET /weather": {
        accepts: [
          {
            scheme: "exact",
            price: "$0.001",
            network: "eip155:84532", // Base Sepolia
            payTo: evmAddress,
          },
          {
            scheme: "exact",
            price: "$0.001",
            network: "solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1", // Solana Devnet
            payTo: svmAddress,
          },
        ],
        description: "Weather data",
        mimeType: "application/json",
      },
    },
    new x402ResourceServer(facilitatorClient)
      .register("eip155:84532", new ExactEvmScheme())
      .register("solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1", new ExactSvmScheme()),
  ),
);

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

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

Full example in the repo here.

import Fastify from "fastify";
import { paymentMiddleware, x402ResourceServer } from "@x402/fastify";
import { ExactEvmScheme } from "@x402/evm/exact/server";
import { ExactSvmScheme } from "@x402/svm/exact/server";
import { HTTPFacilitatorClient } from "@x402/core/server";

const app = Fastify();
const evmAddress = "0xYourEvmAddress";
const svmAddress = "YourSolanaAddress";

const facilitatorClient = new HTTPFacilitatorClient({
  url: "https://x402.org/facilitator"
});

paymentMiddleware(
  app,
  {
    "GET /weather": {
      accepts: [
        {
          scheme: "exact",
          price: "$0.001",
          network: "eip155:84532", // Base Sepolia
          payTo: evmAddress,
        },
        {
          scheme: "exact",
          price: "$0.001",
          network: "solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1", // Solana Devnet
          payTo: svmAddress,
        },
      ],
      description: "Weather data",
      mimeType: "application/json",
    },
  },
  new x402ResourceServer(facilitatorClient)
    .register("eip155:84532", new ExactEvmScheme())
    .register("solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1", new ExactSvmScheme()),
);

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

app.listen({ port: 4021 });

Full example in the repo here.

package main

import (
    "net/http"
    "time"

    x402 "github.com/x402-foundation/x402/go"
    x402http "github.com/x402-foundation/x402/go/http"
    ginmw "github.com/x402-foundation/x402/go/http/gin"
    evm "github.com/x402-foundation/x402/go/mechanisms/evm/exact/server"
    svm "github.com/x402-foundation/x402/go/mechanisms/svm/exact/server"
    "github.com/gin-gonic/gin"
)

func main() {
    evmAddress := "0xYourEvmAddress"
    svmAddress := "YourSolanaAddress"
    evmNetwork := x402.Network("eip155:84532")                              // Base Sepolia
    svmNetwork := x402.Network("solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1")  // Solana Devnet

    r := gin.Default()

    // Create facilitator client
    facilitatorClient := x402http.NewHTTPFacilitatorClient(&x402http.FacilitatorConfig{
        URL: "https://x402.org/facilitator",
    })

    // Apply x402 payment middleware
    r.Use(ginmw.X402Payment(ginmw.Config{
        Routes: x402http.RoutesConfig{
            "GET /weather": {
                Accepts: x402http.PaymentOptions{
                    {
                        Scheme:  "exact",
                        Price:   "$0.001",
                        Network: "eip155:84532",
                        PayTo:   evmAddress,
                    },
                    {
                        Scheme:  "exact",
                        Price:   "$0.001",
                        Network: "solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1",
                        PayTo:   svmAddress,
                    },
                },
                Description: "Get weather data for a city",
                MimeType:    "application/json",
            },
        },
        Facilitator: facilitatorClient,
        Schemes: []ginmw.SchemeConfig{
            {Network: evmNetwork, Server: evm.NewExactEvmScheme()},
            {Network: svmNetwork, Server: svm.NewExactSvmScheme()},
        },
        Timeout: 30 * time.Second,
    }))

    // Protected endpoint
    r.GET("/weather", func(c *gin.Context) {
        c.JSON(http.StatusOK, gin.H{
            "weather":     "sunny",
            "temperature": 70,
        })
    })

    r.Run(":4021")
}

Full example in the repo here.

package main

import (
    "encoding/json"
    "net/http"
    "time"

    x402 "github.com/x402-foundation/x402/go"
    x402http "github.com/x402-foundation/x402/go/http"
    nethttpmw "github.com/x402-foundation/x402/go/http/nethttp"
    evm "github.com/x402-foundation/x402/go/mechanisms/evm/exact/server"
    svm "github.com/x402-foundation/x402/go/mechanisms/svm/exact/server"
)

func main() {
    evmAddress := "0xYourEvmAddress"
    svmAddress := "YourSolanaAddress"
    evmNetwork := x402.Network("eip155:84532")                              // Base Sepolia
    svmNetwork := x402.Network("solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1")  // Solana Devnet

    // Create facilitator client
    facilitatorClient := x402http.NewHTTPFacilitatorClient(&x402http.FacilitatorConfig{
        URL: "https://x402.org/facilitator",
    })

    // Configure routes
    routes := x402http.RoutesConfig{
        "GET /weather": {
            Accepts: x402http.PaymentOptions{
                {
                    Scheme:  "exact",
                    Price:   "$0.001",
                    Network: "eip155:84532",
                    PayTo:   evmAddress,
                },
                {
                    Scheme:  "exact",
                    Price:   "$0.001",
                    Network: "solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1",
                    PayTo:   svmAddress,
                },
            },
            Description: "Get weather data for a city",
            MimeType:    "application/json",
        },
    }

    // Create ServeMux and register handlers
    mux := http.NewServeMux()

    // Protected endpoint
    mux.HandleFunc("GET /weather", func(w http.ResponseWriter, r *http.Request) {
        w.Header().Set("Content-Type", "application/json")
        w.WriteHeader(http.StatusOK)
        json.NewEncoder(w).Encode(map[string]interface{}{
            "weather":     "sunny",
            "temperature": 70,
        })
    })

    // Apply x402 payment middleware
    handler := nethttpmw.X402Payment(nethttpmw.Config{
        Routes:      routes,
        Facilitator: facilitatorClient,
        Schemes: []nethttpmw.SchemeConfig{
            {Network: evmNetwork, Server: evm.NewExactEvmScheme()},
            {Network: svmNetwork, Server: svm.NewExactSvmScheme()},
        },
        Timeout: 30 * time.Second,
    })(mux)

    http.ListenAndServe(":4021", handler)
}

Full example in the repo here.

package main

import (
    "net/http"
    "time"

    x402 "github.com/x402-foundation/x402/go"
    x402http "github.com/x402-foundation/x402/go/http"
    echomw "github.com/x402-foundation/x402/go/http/echo"
    evm "github.com/x402-foundation/x402/go/mechanisms/evm/exact/server"
    svm "github.com/x402-foundation/x402/go/mechanisms/svm/exact/server"
    "github.com/labstack/echo/v4"
)

func main() {
    evmAddress := "0xYourEvmAddress"
    svmAddress := "YourSolanaAddress"
    evmNetwork := x402.Network("eip155:84532")                              // Base Sepolia
    svmNetwork := x402.Network("solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1")  // Solana Devnet

    e := echo.New()

    // Create facilitator client
    facilitatorClient := x402http.NewHTTPFacilitatorClient(&x402http.FacilitatorConfig{
        URL: "https://x402.org/facilitator",
    })

    // Apply x402 payment middleware
    e.Use(echomw.X402Payment(echomw.Config{
        Routes: x402http.RoutesConfig{
            "GET /weather": {
                Accepts: x402http.PaymentOptions{
                    {
                        Scheme:  "exact",
                        Price:   "$0.001",
                        Network: "eip155:84532",
                        PayTo:   evmAddress,
                    },
                    {
                        Scheme:  "exact",
                        Price:   "$0.001",
                        Network: "solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1",
                        PayTo:   svmAddress,
                    },
                },
                Description: "Get weather data for a city",
                MimeType:    "application/json",
            },
        },
        Facilitator: facilitatorClient,
        Schemes: []echomw.SchemeConfig{
            {Network: evmNetwork, Server: evm.NewExactEvmScheme()},
            {Network: svmNetwork, Server: svm.NewExactSvmScheme()},
        },
        Timeout: 30 * time.Second,
    }))

    // Protected endpoint
    e.GET("/weather", func(c echo.Context) error {
        return c.JSON(http.StatusOK, map[string]interface{}{
            "weather":     "sunny",
            "temperature": 70,
        })
    })

    e.Start(":4021")
}

Full example in the repo here.

from typing import Any

from fastapi import FastAPI

from x402.http import FacilitatorConfig, HTTPFacilitatorClient, PaymentOption
from x402.http.middleware.fastapi import PaymentMiddlewareASGI
from x402.http.types import RouteConfig
from x402.mechanisms.evm.exact import ExactEvmServerScheme
from x402.mechanisms.svm.exact import ExactSvmServerScheme
from x402.schemas import Network
from x402.server import x402ResourceServer

app = FastAPI()

# Your receiving wallet addresses
evm_address = "0xYourEvmAddress"
svm_address = "YourSolanaAddress"
EVM_NETWORK: Network = "eip155:84532"  # Base Sepolia
SVM_NETWORK: Network = "solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1"  # Solana Devnet

# Create facilitator client (testnet)
facilitator = HTTPFacilitatorClient(
    FacilitatorConfig(url="https://x402.org/facilitator")
)

# Create resource server and register schemes
server = x402ResourceServer(facilitator)
server.register(EVM_NETWORK, ExactEvmServerScheme())
server.register(SVM_NETWORK, ExactSvmServerScheme())

# Define protected routes
routes: dict[str, RouteConfig] = {
    "GET /weather": RouteConfig(
        accepts=[
            PaymentOption(
                scheme="exact",
                pay_to=evm_address,
                price="$0.001",
                network=EVM_NETWORK,
            ),
            PaymentOption(
                scheme="exact",
                pay_to=svm_address,
                price="$0.001",
                network=SVM_NETWORK,
            ),
        ],
        mime_type="application/json",
        description="Weather report",
    ),
}

# Add payment middleware
app.add_middleware(PaymentMiddlewareASGI, routes=routes, server=server)


@app.get("/weather")
async def get_weather() -> dict[str, Any]:
    return {
        "report": {
            "weather": "sunny",
            "temperature": 70,
        }
    }


if __name__ == "__main__":
    import uvicorn
    uvicorn.run(app, host="0.0.0.0", port=4021)

Full example in the repo here.

from flask import Flask, jsonify

from x402.http import FacilitatorConfig, HTTPFacilitatorClientSync, PaymentOption
from x402.http.middleware.flask import payment_middleware
from x402.http.types import RouteConfig
from x402.mechanisms.evm.exact import ExactEvmServerScheme
from x402.mechanisms.svm.exact import ExactSvmServerScheme
from x402.schemas import Network
from x402.server import x402ResourceServerSync

app = Flask(__name__)

# Your receiving wallet addresses
evm_address = "0xYourEvmAddress"
svm_address = "YourSolanaAddress"
EVM_NETWORK: Network = "eip155:84532"  # Base Sepolia
SVM_NETWORK: Network = "solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1"  # Solana Devnet

facilitator = HTTPFacilitatorClientSync(
    FacilitatorConfig(url="https://x402.org/facilitator")
)

server = x402ResourceServerSync(facilitator)
server.register(EVM_NETWORK, ExactEvmServerScheme())
server.register(SVM_NETWORK, ExactSvmServerScheme())

routes: dict[str, RouteConfig] = {
    "GET /weather": RouteConfig(
        accepts=[
            PaymentOption(
                scheme="exact",
                pay_to=evm_address,
                price="$0.001",
                network=EVM_NETWORK,
            ),
            PaymentOption(
                scheme="exact",
                pay_to=svm_address,
                price="$0.001",
                network=SVM_NETWORK,
            ),
        ],
        mime_type="application/json",
        description="Weather report",
    ),
}

payment_middleware(app, routes=routes, server=server)


@app.route("/weather")
def get_weather():
    return jsonify({
        "report": {
            "weather": "sunny",
            "temperature": 70,
        }
    })


if __name__ == "__main__":
    app.run(host="0.0.0.0", port=4021)

Route Configuration Interface:

interface RouteConfig {
  accepts: Array<{
    scheme: string;           // Payment scheme: "exact" or "upto"
    price: string;            // For "exact": the fixed price. For "upto": the maximum authorized amount.
    network: string;          // Network in CAIP-2 format (e.g., "eip155:84532" or "solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1")
    payTo: string;            // Your wallet address
  }>;
  description?: string;       // Description of the resource
  mimeType?: string;          // MIME type of the response
  extensions?: object;        // Optional extensions (e.g., Bazaar)
}

When a request is made to these routes without payment, your server will respond with the HTTP 402 Payment Required code and payment instructions.

Payment Schemes: Exact vs Upto

x402 supports two payment schemes that control how charges are calculated: exact (default) — The client pays the exact advertised price. This is the simplest scheme and works across all networks (EVM, SVM, Stellar, Aptos) and all SDKs (TypeScript, Go, Python). Best for fixed-price endpoints where the cost is known upfront. upto — The client authorizes a maximum amount, but the server settles only what was actually used. This enables usage-based billing where the final charge depends on work performed (LLM token count, compute time, bytes served, etc.). Currently available on EVM networks only (Permit2), in TypeScript, Go, and Python SDKs. The examples in step 2 above all use the exact scheme. To use upto instead, there are two key differences:

Set scheme: "upto" in your route config, where price becomes the maximum the client authorizes
Call setSettlementOverrides in your handler to specify the actual amount to charge

Express
Go (Gin)
FastAPI

Full example in the repo here.

import express from "express";
import { paymentMiddleware, setSettlementOverrides, x402ResourceServer } from "@x402/express";
import { UptoEvmScheme } from "@x402/evm/upto/server";
import { HTTPFacilitatorClient } from "@x402/core/server";

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

const facilitatorClient = new HTTPFacilitatorClient({
  url: "https://x402.org/facilitator"
});

const maxPrice = "$0.10"; // Maximum the client authorizes (10 cents)

app.use(
  paymentMiddleware(
    {
      "GET /api/generate": {
        accepts: {
          scheme: "upto",
          price: maxPrice,
          network: "eip155:84532", // Base Sepolia
          payTo: evmAddress,
        },
        description: "AI text generation — billed by token usage",
        mimeType: "application/json",
      },
    },
    new x402ResourceServer(facilitatorClient)
      .register("eip155:84532", new UptoEvmScheme()),
  ),
);

app.get("/api/generate", (req, res) => {
  // Simulate variable-cost work (LLM tokens, compute time, etc.)
  const maxAmountAtomic = 100000; // 10 cents in 6-decimal USDC atomic units
  const actualUsage = Math.floor(Math.random() * (maxAmountAtomic + 1));

  // Settle only the actual usage — the client is never charged more than this
  setSettlementOverrides(res, { amount: String(actualUsage) });

  res.json({
    result: "Here is your generated text...",
    usage: {
      authorizedMaxAtomic: String(maxAmountAtomic),
      actualChargedAtomic: String(actualUsage),
    },
  });
});

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

Full example in the repo here.

package main

import (
    "fmt"
    "math/rand"
    "net/http"
    "time"

    x402 "github.com/x402-foundation/x402/go"
    x402http "github.com/x402-foundation/x402/go/http"
    ginmw "github.com/x402-foundation/x402/go/http/gin"
    uptoevm "github.com/x402-foundation/x402/go/mechanisms/evm/upto/server"
    "github.com/gin-gonic/gin"
)

func main() {
    evmAddress := "0xYourEvmAddress"
    evmNetwork := x402.Network("eip155:84532") // Base Sepolia

    r := gin.Default()

    facilitatorClient := x402http.NewHTTPFacilitatorClient(&x402http.FacilitatorConfig{
        URL: "https://x402.org/facilitator",
    })

    maxPrice := "$0.10" // Maximum the client authorizes

    r.Use(ginmw.X402Payment(ginmw.Config{
        Routes: x402http.RoutesConfig{
            "GET /api/generate": {
                Accepts: x402http.PaymentOptions{
                    {
                        Scheme:  "upto",
                        Price:   maxPrice,
                        Network: evmNetwork,
                        PayTo:   evmAddress,
                    },
                },
                Description: "AI text generation - billed by token usage",
                MimeType:    "application/json",
            },
        },
        Facilitator: facilitatorClient,
        Schemes: []ginmw.SchemeConfig{
            {Network: evmNetwork, Server: uptoevm.NewUptoEvmScheme()},
        },
        Timeout: 30 * time.Second,
    }))

    r.GET("/api/generate", func(c *gin.Context) {
        // Simulate variable-cost work (LLM tokens, compute time, etc.)
        maxAmountAtomic := 100000 // 10 cents in 6-decimal USDC atomic units
        actualUsage := rand.Intn(maxAmountAtomic + 1)

        // Settle only the actual usage
        ginmw.SetSettlementOverrides(c, &x402.SettlementOverrides{
            Amount: fmt.Sprintf("%d", actualUsage),
        })

        c.JSON(http.StatusOK, gin.H{
            "result": "Here is your generated text...",
            "usage": gin.H{
                "authorizedMaxAtomic": fmt.Sprintf("%d", maxAmountAtomic),
                "actualChargedAtomic": fmt.Sprintf("%d", actualUsage),
            },
        })
    })

    r.Run(":4021")
}

import random
from typing import Any

from fastapi import FastAPI
from starlette.responses import Response

from x402.http import FacilitatorConfig, HTTPFacilitatorClient, PaymentOption
from x402.http.middleware.fastapi import PaymentMiddlewareASGI, set_settlement_overrides
from x402.http.types import RouteConfig
from x402.mechanisms.evm.upto import UptoEvmServerScheme
from x402.schemas import Network
from x402.server import x402ResourceServer

app = FastAPI()

evm_address = "0xYourEvmAddress"
EVM_NETWORK: Network = "eip155:84532"  # Base Sepolia

facilitator = HTTPFacilitatorClient(
    FacilitatorConfig(url="https://x402.org/facilitator")
)

server = x402ResourceServer(facilitator)
server.register(EVM_NETWORK, UptoEvmServerScheme())

max_price = "$0.10"  # Maximum the client authorizes (10 cents)

routes: dict[str, RouteConfig] = {
    "GET /api/generate": RouteConfig(
        accepts=[
            PaymentOption(
                scheme="upto",
                pay_to=evm_address,
                price=max_price,
                network=EVM_NETWORK,
            ),
        ],
        mime_type="application/json",
        description="AI text generation — billed by token usage",
    ),
}

app.add_middleware(PaymentMiddlewareASGI, routes=routes, server=server)


@app.get("/api/generate")
async def generate(response: Response) -> dict[str, Any]:
    # Simulate variable-cost work (LLM tokens, compute time, etc.)
    max_amount_atomic = 100000  # 10 cents in 6-decimal USDC atomic units
    actual_usage = random.randint(0, max_amount_atomic)

    # Settle only the actual usage — the client is never charged more than this
    set_settlement_overrides(response, {"amount": str(actual_usage)})

    return {
        "result": "Here is your generated text...",
        "usage": {
            "authorizedMaxAtomic": str(max_amount_atomic),
            "actualChargedAtomic": str(actual_usage),
        },
    }


if __name__ == "__main__":
    import uvicorn
    uvicorn.run(app, host="0.0.0.0", port=4021)

The setSettlementOverrides amount supports three formats:

Raw atomic units — e.g., "1000" settles exactly 1,000 atomic units of the token (for USDC with 6 decimals, "1000" = $0.001)
Percentage of authorized maximum — e.g., "50%" settles 50% of PaymentRequirements.amount. Supports up to two decimal places (e.g., "33.33%"). The result is floored to the nearest atomic unit.
Dollar price — e.g., "$0.05" converts a USD-denominated price to atomic units. This format works when you configured your route with $-prefixed pricing (e.g., price: "$0.10"). Token decimals are determined from the registered scheme. The result is rounded to the nearest atomic unit.

The resolved amount must always be <= the authorized maximum. If the amount is "0", no on-chain transaction occurs and the client is not charged.

3. Test Your Integration

To verify:

Make a request to your endpoint (e.g., curl http://localhost:4021/weather).
The server responds with a 402 Payment Required, including payment instructions in the PAYMENT-REQUIRED header.
Complete the payment using a compatible client, wallet, or automated agent. This typically involves signing a payment payload, which is handled by the client SDK detailed in the Quickstart for Buyers.
Retry the request, this time including the PAYMENT-SIGNATURE header containing the cryptographic proof of payment.
The server verifies the payment via the facilitator and, if valid, returns your actual API response (e.g., { "data": "Your paid API response." }).

4. Enhance Discovery with Metadata (Recommended)

When using a facilitator that supports the Bazaar extension, your endpoints can be listed in the x402 Bazaar, the discovery layer that helps buyers and AI agents find services. For HTTP endpoints, add the discovery extension to your route config:

import { declareDiscoveryExtension } from "@x402/extensions/bazaar";

{
  "GET /weather": {
    accepts: [{ scheme: "exact", price: "$0.001", network: "eip155:8453", payTo: "0xYourAddress" }],
    description: "Get real-time weather data including temperature, conditions, and humidity",
    mimeType: "application/json",
    extensions: {
      ...declareDiscoveryExtension({
        input: { city: "San Francisco" },
        inputSchema: {
          properties: { city: { type: "string", description: "City name" } },
          required: ["city"],
        },
      }),
    },
  },
}

For MCP tools, pass the discovery extension in your payment wrapper config:

import { createPaymentWrapper } from "@x402/mcp";
import { declareDiscoveryExtension } from "@x402/extensions/bazaar";

const paid = createPaymentWrapper(resourceServer, {
  accepts,
  resource: { url: "mcp://tool/get_weather", description: "Get current weather for a city" },
  extensions: declareDiscoveryExtension({
    toolName: "get_weather",
    description: "Get current weather for a city",
    transport: "sse",
    inputSchema: {
      properties: { city: { type: "string", description: "City name" } },
      required: ["city"],
    },
  }),
});

Learn more about the discovery layer in the Bazaar documentation.

5. Error Handling

If you run into trouble, check out the examples in the repo for more context and full code.
Run npm install or go mod tidy to install dependencies

Running on Mainnet

Once you’ve tested your integration on testnet, you’re ready to accept real payments on mainnet.

1. Update the Facilitator URL

For mainnet, use a production facilitator. See the x402 Ecosystem for available options. Example using one facilitator:

Node.js
Go (Gin)
Go (Echo)
Python (FastAPI)
Python (Flask)

const facilitatorClient = new HTTPFacilitatorClient({
  url: "https://api.cdp.coinbase.com/platform/v2/x402"
  // url: "https://facilitator.payai.network"  // PayAI Facilitator
});

facilitatorClient := x402http.NewHTTPFacilitatorClient(&x402http.FacilitatorConfig{
    URL: "https://api.cdp.coinbase.com/platform/v2/x402",
    // URL: "https://facilitator.payai.network",  // PayAI Facilitator
})

facilitatorClient := x402http.NewHTTPFacilitatorClient(&x402http.FacilitatorConfig{
    URL: "https://api.cdp.coinbase.com/platform/v2/x402",
    // URL: "https://facilitator.payai.network",  // PayAI Facilitator
})

from x402.http import FacilitatorConfig, HTTPFacilitatorClient

facilitator = HTTPFacilitatorClient(
    FacilitatorConfig(url="https://api.cdp.coinbase.com/platform/v2/x402")
    #FacilitatorConfig(url="https://facilitator.payai.network")  # PayAI Facilitator
)

from x402.http import FacilitatorConfig, HTTPFacilitatorClientSync

facilitator = HTTPFacilitatorClientSync(
    FacilitatorConfig(url="https://api.cdp.coinbase.com/platform/v2/x402")
    #FacilitatorConfig(url="https://facilitator.payai.network")  # PayAI Facilitator
)

2. Update Your Network Identifier

Change from testnet to mainnet network identifiers:

Base Mainnet
Solana Mainnet
Multi-Network

// Testnet → Mainnet
network: "eip155:8453", // Base mainnet (was eip155:84532)

// Testnet → Mainnet
network: "solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp", // Solana mainnet

// For Solana, use a Solana wallet address (base58 format)
payTo: "YourSolanaWalletAddress",

// Support multiple networks on the same endpoint
{
  "GET /weather": {
    accepts: [
      {
        scheme: "exact",
        price: "$0.001",
        network: "eip155:8453",  // Base mainnet
        payTo: "0xYourEvmAddress",
      },
      {
        scheme: "exact",
        price: "$0.001",
        network: "solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp",  // Solana mainnet
        payTo: "YourSolanaAddress",
      },
    ],
    description: "Weather data",
  },
}

3. Register Multiple Schemes (Multi-Network)

For multi-network support, register both EVM and SVM schemes:

Express / Hono / Fastify
Go (Gin)
Go (Echo)
Python

import { ExactEvmScheme } from "@x402/evm/exact/server";
import { ExactSvmScheme } from "@x402/svm/exact/server";

const server = new x402ResourceServer(facilitatorClient);
server.register("eip155:*", new ExactEvmScheme());
server.register("solana:*", new ExactSvmScheme());

import (
    evm "github.com/x402-foundation/x402/go/mechanisms/evm/exact/server"
    svm "github.com/x402-foundation/x402/go/mechanisms/svm/exact/server"
)

r.Use(ginmw.X402Payment(ginmw.Config{
    // ...
    Schemes: []ginmw.SchemeConfig{
        {Network: x402.Network("eip155:8453"), Server: evm.NewExactEvmScheme()},
        {Network: x402.Network("solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp"), Server: svm.NewExactSvmScheme()},
    },
}))

import (
    evm "github.com/x402-foundation/x402/go/mechanisms/evm/exact/server"
    svm "github.com/x402-foundation/x402/go/mechanisms/svm/exact/server"
)

e.Use(echomw.X402Payment(echomw.Config{
    // ...
    Schemes: []echomw.SchemeConfig{
        {Network: x402.Network("eip155:8453"), Server: evm.NewExactEvmScheme()},
        {Network: x402.Network("solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp"), Server: svm.NewExactSvmScheme()},
    },
}))

from x402.mechanisms.evm.exact import ExactEvmServerScheme
from x402.mechanisms.svm.exact import ExactSvmServerScheme
from x402.server import x402ResourceServer

server = x402ResourceServer(facilitator)
server.register("eip155:8453", ExactEvmServerScheme())  # Base mainnet
server.register("solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp", ExactSvmServerScheme())  # Solana mainnet

4. Update Your Wallet

Make sure your receiving wallet address is a real mainnet address where you want to receive USDC payments.

5. Test with Real Payments

Before going live:

Test with small amounts first
Verify payments are arriving in your wallet
Monitor the facilitator for any issues

Warning: Mainnet transactions involve real money. Always test thoroughly on testnet first and start with small amounts on mainnet.

Network Identifiers (CAIP-2)

x402 v2 uses CAIP-2 format for network identifiers:

Network	CAIP-2 Identifier
Base Mainnet	`eip155:8453`
Base Sepolia	`eip155:84532`
Solana Mainnet	`solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp`
Solana Devnet	`solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1`

See Network Support for the full list.

Next Steps

Check out the Advanced Example for a more complex payment flow
Explore Advanced Concepts like lifecycle hooks for custom logic before/after verification/settlement
Explore Extensions like Bazaar for service discovery
Get started as a buyer

For questions or support, join our Discord.

Summary

This quickstart covered:

Installing the x402 SDK and relevant middleware
Adding payment middleware to your API and configuring it
Choosing between exact (fixed-price) and upto (usage-based) payment schemes
Testing your integration
Deploying to mainnet with CAIP-2 network identifiers

Your API is now ready to accept crypto payments through x402.

Welcome

Getting Started

Core Concepts

Extensions

Advanced Concepts

Guides

SDK Features

Quickstart for Sellers

Prerequisites

1. Install Dependencies

2. Add Payment Middleware

Payment Schemes: Exact vs Upto

3. Test Your Integration

4. Enhance Discovery with Metadata (Recommended)

5. Error Handling

Running on Mainnet

1. Update the Facilitator URL

2. Update Your Network Identifier

3. Register Multiple Schemes (Multi-Network)

4. Update Your Wallet

5. Test with Real Payments

Network Identifiers (CAIP-2)

Next Steps

Summary

Welcome

Getting Started

Core Concepts

Extensions

Advanced Concepts

Guides

SDK Features

Documentation Index

​Prerequisites

​1. Install Dependencies

​2. Add Payment Middleware

​Payment Schemes: Exact vs Upto

​3. Test Your Integration

​4. Enhance Discovery with Metadata (Recommended)

​5. Error Handling

​Running on Mainnet

​1. Update the Facilitator URL

​2. Update Your Network Identifier

​3. Register Multiple Schemes (Multi-Network)

​4. Update Your Wallet

​5. Test with Real Payments

​Network Identifiers (CAIP-2)

​Next Steps

​Summary

Prerequisites

1. Install Dependencies

2. Add Payment Middleware

Payment Schemes: Exact vs Upto

3. Test Your Integration

4. Enhance Discovery with Metadata (Recommended)

5. Error Handling

Running on Mainnet

1. Update the Facilitator URL

2. Update Your Network Identifier

3. Register Multiple Schemes (Multi-Network)

4. Update Your Wallet

5. Test with Real Payments

Network Identifiers (CAIP-2)

Next Steps

Summary