Implement an x402-capable server endpoint so AI agents can pay per API call with stablecoins without accounts or sessions

Steps

1. Install the x402 server library for your runtime (npm install x402 for Node/Express, or pip install x402 for Python/FastAPI); the reference implementations are published at github.com/coinbase/x402 under Apache 2.0.
2. Add the x402 middleware to your route: on an unauthenticated request, return HTTP 402 with payment instructions encoded in the X402-Payment-Required header specifying accepted token (e.g., USDC on Base), amount, and your receiving wallet address.
3. Configure a facilitator (Coinbase CDP or Cloudflare's x402 edge) to verify incoming payment proofs; the facilitator checks on-chain settlement and returns a verification token to your server.
4. On the client's retry request (which carries the X402-Payment header with the signed payment payload), call facilitator.verify() and, if valid, serve the protected resource with a 200 OK and include the receipt in the X402-Receipt response header.
5. Test end-to-end in a local sandbox using the x402 testnet mode with USDC on Base Sepolia before pointing to mainnet USDC.