Design a payment processing system

Q: Design a payment processing system

This question evaluates system-design competency in building reliable payment workflows, covering distributed transaction handling, idempotent APIs, asynchronous external integrations, and accounting/ledger correctness.

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System Design questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master system design interviews.

Question

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Scenario

Design a backend payment system for an online product that supports:

One-time charges and refunds.
Idempotent payment APIs (clients may retry).
Asynchronous interaction with external payment processors (e.g., card networks via a payment gateway).
Accurate accounting/ledger and reporting.

What to cover

Core APIs and data model.
Handling retries, duplicates, and failures.
Ensuring correctness (no double charge; consistent ledger).
Observability and reconciliation.

You can make reasonable assumptions and state them explicitly.

Design a payment processing system

Scenario

What to cover

Solution

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Design a payment processing system

Overview

Scenario

What to cover

Solution

Comments (0)