Building Paid API Endpoints with x402 and agentwallet-sdk: A Developer Guide

Building Paid API Endpoints with x402 and agentwallet-sdk: A Developer Guide AI Disclosure: This article was drafted with AI assistance and reviewed for technical accuracy. The HTTP spec has a status code that has gone mostly unused for 30 years: 402 Payment Required . The x402 protocol finally puts it to work -- and if you are building APIs that autonomous agents will consume, this changes everything. What x402 Actually Is x402 is an HTTP-native payment protocol. When a client hits a paid endpoint without funds attached, the server returns a 402 response with a machine-readable payment payload. The client pays, retries the request with proof of payment, and gets the resource. No redirects. No OAuth dance. No separate billing API. Coinbase has run x402 in production for several months. The numbers are public: over 115 million micropayments processed. Stripe recently announced integration support, which means x402 is crossing from "experimental Web3 thing" into mainstream infrastructure