MPP - Machine Payments Protocol

MPP is an open protocol (co-authored by Tempo and Stripe) that standardizes HTTP 402 Payment Required for machine-to-machine payments. Clients pay in the same HTTP request - no accounts, API keys, or checkout flows needed.

The core protocol spec is submitted to the IETF as the Payment HTTP Authentication Scheme.

Code in this skill uses placeholder token names (<USDC_TEMPO_MAINNET>, <PATHUSD_TESTNET>); the real addresses live in the Tempo documentation and references/tempo-method.md.

Core Architecture

Three primitives power every MPP payment:

1. Challenge - server-issued payment requirement (in WWW-Authenticate: Payment header)
2. Credential - client-submitted payment proof (in Authorization: Payment header)
3. Receipt - server confirmation of successful payment (in Payment-Receipt header)

Payment Methods & Intents

MPP is payment-method agnostic. Each method defines its own settlement rail: