GOAT Flow (goat-x402)

This repository is the public integration reference for GOAT Flow, GOAT Network's x402 payment platform.

What x402 Is Used For

x402 is a payment standard for crypto-native applications.
It allows an app or API to request token payment in a structured way, so users can complete payment from their wallet and the service can verify settlement.

In short, GOAT Flow makes blockchain payments a standard part of application access, checkout, and service flows.

What This Project Provides

This project demonstrates how to integrate x402 in practice, including:

• drop-in hosted checkout for DIRECT and DELEGATE merchants
• order creation and browser wallet payment workflows
• TypeScript and Go server SDK integration
• QuickPay payer/agent tooling and MPP receipt middleware
• callback/settlement contracts and a runnable demo

Choose an Integration

Need	Start here
Hosted browser checkout	docs/x402-checkout.md and goatflow-checkout
Custom wallet/order UI	goatflow-sdk + goatflow-sdk-server (TypeScript package or Go source)
Agent or CLI payment	goatflow-quickpay
Verify MPP receipts in an API	@goatnetwork/mpp-middleware or Go source
Callback contracts	goatx402-contract

Hosted Checkout has two server-authoritative forms under one Checkout Sessions API: DIRECT uses a decimal price; DELEGATE uses either cross-chain decimal price mode or the compatibility single-chain fixed_amount_wei mode. Fixed DIRECT QuickPay products can also be opened without a merchant backend.

Public Modules

Package / module	Source	Purpose
goatflow-checkout	goatx402-checkout	Framework-free popup/tab/redirect browser SDK
goatflow-sdk	goatx402-sdk	Low-level EVM wallet payment and MPP client primitives
goatflow-sdk-server	goatx402-sdk-server-ts	HMAC-authenticated TypeScript server SDK
Go server SDK (source-only)	goatx402-sdk-server-go	HMAC-authenticated Go SDK; clone this repo and use a local replace
goatflow-quickpay	goatx402-quickpay	Manifest-driven payer/agent library and CLI
@goatnetwork/mpp-middleware	goatx402-mpp-middleware-ts	Express/Fastify MPP receipt verification
Go MPP middleware (source-only)	goatx402-mpp-middleware-go	Go HTTP receipt verification; clone this repo and use a local replace
Contracts	goatx402-contract	MerchantCallback, TopupCallback, and test tokens
Demo	goatx402-demo	Hosted Checkout plus advanced Classic/MPP examples

Chain Support

GOAT Flow supports configured EVM mainnet chains. Each merchant still needs per-chain token, fee, receiving-address, and callback-contract configuration before taking payments on a chain.

Chain	Chain ID	DIRECT	DELEGATE
Ethereum	1	Yes	Yes
Polygon	137	Yes	Yes
BSC	56	Yes	Yes
Arbitrum	42161	Yes	Yes
Optimism	10	Yes	Yes
Avalanche	43114	Yes	Yes
Base	8453	Yes	Yes
Berachain	80094	Yes	Yes
X Layer	196	Yes	Yes
GOAT	2345	Yes	Yes
Metis	1088	Yes	No
Tempo	4217	Yes	No

DIRECT means the payer transfers ERC-20 tokens directly to the merchant receiving address. DELEGATE means EIP-3009 or Permit2 settlement through the merchant callback contract and TSS submission. The table describes merchant settlement chains: Metis and Tempo are DIRECT-only there. Eligible cross-chain DELEGATE source payments are derived from live token/TSS configuration.

Development Documentation

Use docs/README.md as the canonical documentation hub.

Quick references:

• DEVELOPER_FAST.md - concise SDK/backend integration guide.
• API.md - Core API and HMAC authentication reference.
• docs/x402-checkout.md - hosted Checkout Sessions and browser SDK.
• docs/README.md - structured public docs index, including QuickPay, Checkout, MPP, and agent integration paths.

Production API base URL: https://flow-api.goat.network.

License

No license has been declared for this repository as a whole. Unless and until one is added, all rights are reserved by the project owners (GOAT Network); contact them before any external use or redistribution. Exception: the four npm packages — goatflow-sdk, goatflow-sdk-server, goatflow-quickpay, and goatflow-checkout — are each MIT-licensed (see the LICENSE file inside their source directories).