Design a Payment Processing System
Company: OpenAI
Role: Software Engineer
Category: System Design
Difficulty: hard
Interview Round: Onsite
Overview: This system design question evaluates a candidate's ability to architect a backend payment system that stays correct under retries, concurrency, and partial failure. It tests practical application of idempotency, double-entry ledgers, and asynchronous webhook handling, commonly asked to assess distributed-systems reasoning around financial correctness and auditability.