Design a Payment Processing System

Company: OpenAI

Role: Software Engineer

Category: System Design

Difficulty: hard

Interview Round: Onsite

Quick Answer: 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.