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Express.js Server Example with X402 Payment Support

This example demonstrates how to create an Express.js API server with X402 payment requirements for specific endpoints.

Features

  • Free endpoints - Public access without payment
  • Premium endpoints - Require payment to access
  • Automatic payment verification - Built-in Solana blockchain verification
  • Flexible pricing - Different amounts for different endpoints
  • TypeScript - Full type safety

Setup

1. Install Dependencies

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npm install

2. Configure Environment

Create a .env file based on .env.example:

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cp .env.example .env

Edit .env with your Solana wallet details:

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PAYMENT_WALLET_ADDRESS=your_solana_wallet_address_here
USDC_MINT_ADDRESS=EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v
SOLANA_RPC_URL=https://api.devnet.solana.com
PORT=3000

3. Build and Run

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# Build TypeScript
npm run build

# Start server
npm start

# Or run in development mode
npm run dev

The server will start on http://localhost:3000.

API Endpoints

Free Endpoints

  • GET / - API information (no payment)
  • GET /free-data - Free data access (no payment)
  • GET /premium-data - Premium data (0.10 USDC)
  • GET /expensive-data - AI inference (1.00 USDC)
  • GET /tiered-data/:tier - Tiered content (0.05 USDC)
  • POST /process-data - Data processing (0.25 USDC)

Usage Examples

Free Endpoint

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curl http://localhost:3000/free-data

Response: 

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{
  "data": "This is free content available to everyone",
  "price": 0,
  "access": "public"
}


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curl http://localhost:3000/premium-data

Response (402 Payment Required): ```json { "max_amount_required": "0.10", "asset_type": "SPL", "asset_address": "DEMO_USDC_MINT", "payment_address": "DEMO_WALLET_ADDRESS", "network": "solana-devnet", "expires_at": "2025-01-01T10:05:00Z", "nonce": "...", "payment_id": "...",