Payment Gateway System

Problem Statement

Design a payment gateway system that supports multiple types of credit cards and bank cards. Your clients will have POS (Point of Sale) machines that scan cards and call your API to submit payment requests.

Given Constraints

• Scope: Focus on card validation, not full transaction processing or settlement
• Card types: Visa, Mastercard, American Express, Discover, and major regional cards
• Client interface: POS machines make synchronous HTTPS calls for payment validation
• Compliance: Must handle card data in a PCI-DSS compliant manner
• Latency: Validation responses must be fast enough for in-person checkout (< 200ms)

Disclaimer: This is a sample solution to help you get started. To better prepare for the interview, you should think through the question yourself and try to come up with your own solution. System design questions are open-ended and have multiple valid approaches.