Build a server that responds to HTTP 402 and accepts x402 stablecoin payments so AI agents can pay per API call without accounts or sessions

Steps

1. Review the x402 specification and v2 network/asset identification standard at the x402 Foundation (formalized April 2026 under the Linux Foundation); understand the client-server flow: client requests resource, server returns 402 with a payment-details header, client sends a signed payment payload in a standard HTTP header
2. Configure your server to return a 402 status with a structured JSON body describing the accepted token (e.g., USDC on Base), the amount, and your receiving address or Circle Gateway balance endpoint
3. On the client side, provision a Coinbase Agentic Wallet (launched February 2026) or a CDP Server Wallet v2 (GA July 2025) so the agent has a funded, key-managed wallet capable of signing and broadcasting stablecoin transactions without exposing raw keys
4. After the client submits the signed payment payload in the designated request header, verify the on-chain settlement or Circle Gateway receipt before serving the protected resource
5. Implement idempotency by tying each payment payload to a nonce; reject replays using the nonce even if the underlying transaction confirms twice due to agent retry logic
6. Test with Circle Gateway's nanopayments endpoint, which supports gas-free USDC transfers as small as $0.000001, making it suitable for high-frequency agent API calls