The MPPHub stack has five layers. The protocol is the standard. The blockchain is the developer interface. Understanding all three layers is how you build production-ready pay-per-request systems.
Architecture
L0 ยท PROTOCOL
HTTP 402 - the forgotten standard
HTTP 402 Payment Required has existed in the spec since RFC 2616 (1999). It was reserved for a future where machines could pay machines. That future arrived with programmable blockchains. MPPHub implements the protocol as it was always intended: stateless, RESTful, and composable.
MPP Role
MPPHub defines and implements the header schema, making HTTP 402 concrete for the first time.
Specifications
Status Code
402 Payment Required
Request Header
Payment-Request: solana; amount=...; recipient=...; network=...
Receipt Header
Payment-Receipt: solana; signature=...; network=...
Standard
RFC 7231 compatible
Transport
Pure HTTP - no WebSocket, no streaming