What is how-to-build-a-payment-gateway-for-ai-agents?

This repository is a learning project for builders who want to create a payment system where an AI agent pays a merchant for a resource. It targets one specific problem: how an agent requests something that costs money, how that payment gets approved, how a separate actor carries out the payment on a blockchain, and how the merchant confirms the payment before handing over the resource. It is not a general AI guide, a general crypto guide, or a wallet tutorial. The project connects three pieces. First, it uses a style of payment negotiation called x402, where a merchant responds to an unpaid request with a "payment required" notice. Second, it uses a standard called ERC-3009 for signing token transfers, which lets a payer authorize a payment without directly touching the blockchain. Third, it handles verification on the merchant side, so the merchant can confirm the payment matches the original request and then deliver the paid resource. The core problem it addresses is that existing payment systems assume a human is present at checkout. AI agents work differently. They need machine-readable payment requests, signed authorization, delegated execution where someone else pays the network fee, replay protection so a payment cannot be reused, time limits on validity, and merchant-side checks. The repository is built around these requirements. Inside, you find a Solidity token contract with functions for authorized transfers and cancellations, Foundry tests that verify the contract behavior, and TypeScript integration tests that run the full flow locally. The docs folder explains the payment flow, the signing rules, and the roles of the signer versus the executor. A glossary defines key terms. The repository is upfront about its limits. It does not claim to be a production gateway. It lacks a persistent server, production key management, settlement infrastructure, multi-chain support, and a complete facilitator setup. It is a local, buildable demonstration of a real payment flow shape, meant for understanding the pieces rather than deploying them live.