x402 Protocol Overview

What is x402?

x402 is a payment protocol built on HTTP 402 (Payment Required). When a client requests a paid resource, the server responds with 402 and includes payment requirements in the X-Payment-Required header. The client constructs a payment proof, attaches it as the X-Payment header, and retries the request.

FluxA extends the x402 protocol to support three payment schemes — EVM (USDC on Base), Credits, and XRP — enabling AI agents to pay for APIs, MCP tools, and other resources programmatically.

Payment Schemes

Scheme	Network	Currency	Amount Unit	Signature
EVM	base	USDC	6 decimals (1000000 = 1 USDC)	EIP-712 TransferWithAuthorization
Credits	fluxa-monetize-credits	FLUXA_MONETIZE_CREDITS	2 decimals (100 = 1 Credit)	EIP-712 CreditsMandateSpend
XRP	xrpl-mainnet	XRP	drops (1000000 = 1 XRP)	Signed XRPL Payment transaction

All schemes use x402Version: 1 and scheme: "exact".

How It Works

1. Client sends a request to a paid resource
2. Server responds with HTTP 402 and X-Payment-Required header containing accepted payment schemes
3. Client selects a scheme, constructs a signed payment proof
4. Client retries the request with the X-Payment header
5. Server verifies and settles the payment, then delivers the resource

See Payment Flow for a detailed walkthrough.

Facilitators

Each scheme has a facilitator — a service that verifies payment proofs and executes settlement:

Facilitator	Schemes	Settlement	Base URL
EVM Facilitator	EVM (USDC)	On-chain transferWithAuthorization on Base	https://facilitator.xechoai.xyz/
Credits Facilitator	Credits	Off-chain balance debit with immutable ledger	https://walletapi.fluxapay-qa.xyz/api/facilitator
XRP Facilitator	XRP	On-chain XRPL Payment transaction	https://walletapi.fluxapay-qa.xyz/api/facilitator

Credits and XRP share the same multi-asset facilitator service.

Next Steps

• Payment Flow — end-to-end walkthrough
• EVM Scheme — USDC on Base payment details
• Credits Scheme — FluxA Credits payment details
• XRP Scheme — XRP Ledger payment details