System Design: Payment System

System DesignOpenAILast reported September 2026High Frequency
Reported
53× across candidate reports
First seen
May 2025
Last reported
September 2026
Reported outcome
mixed

Problem Overview

OpenAI system design question, reconstructed from 53 candidate reports (May 2025 to September 2026). Candidates reported 10 follow-ups.

  • 10 candidate-reported follow-ups — the probes candidates report being asked, with the trigger for each
  • The full problem statement — full requirements, constraints, and edge cases
  • Approach and trade-offs — what passing candidates did, and the mistakes that sink people
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Verified Source
Every question is reconstructed from multiple independent candidate reports. Follow-ups candidates reported, not invented ones.
Codex Fact-Checked
Technical claims, formulas, and scale numbers are reviewed against primary sources.
Interviewer Follow-ups
The follow-ups candidates reported, with the trigger that prompts each one — plus the mistakes that sink people.
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