RPP402 is an open commerce protocol for autonomous AI on Robinhood Chain. The official site and docs describe it as a standard that lets AI agents discover services, request pricing, authorize payment, settle commerce onchain, and receive cryptographic proof that the transaction happened. RPP402 v1 is organized around six core primitives: Discovery, Quote, Commerce Session, Payment Intent, Settlement, and Receipt. The project is positioned as protocol infrastructure for machine-to-machine commerce rather than a generic retail payment app.