x402 Protocol v2

Open payment standard enabling clients to pay for external resources over any transport layer (HTTP, MCP, A2A). Protocol version: 2.

Core Concepts

x402 has three architectural layers:

1. Types — PaymentRequirements, PaymentPayload, SettlementResponse, VerifyResponse (transport/scheme-agnostic)
2. Logic — Payment formation, verification, settlement (scheme+network specific, e.g. exact/EVM)
3. Representation — How payment data is transmitted (transport-specific: HTTP headers, JSON-RPC, etc.)

Payment Flow

1. Client requests a protected resource
2. Server responds with Payment Required + PaymentRequired JSON (contains accepts array)
3. Client picks a payment method, signs authorization, sends PaymentPayload
4. Server forwards to facilitator → verify → settle → returns resource + SettlementResponse