# Design a Pricing Service with Reliable Payment Handling Design pricing and payment orchestration emphasizing idempotency, reconciliation, and failure handling rather than supply-demand matching. ### Constraints & Assumptions - Client retries and duplicate callbacks are expected. - Charged amount must bind to an immutable quote. ### Clarifying Questions to Ask - When does a quote expire? - Are authorization and capture separate? ### What a Strong Answer Covers - Quote versions, payment state machine, idempotency, ledger, retries, and reconciliation. ### Follow-up Questions - How are partial refunds handled? - What if capture succeeds after a timeout?