Design
Payment Gateway (Stripe-like)
Design a payment gateway supporting card processing, refunds, fraud detection, and PCI-compliant tokenization at scale.
This is a Low-Level Design (LLD) problem. New to LLD vs HLD? Start here.
01 - Why interviewers ask this
Payment correctness under failure is the whole point — interviewers specifically test idempotency (never double-charge on a retried request) and rigorous state tracking.
02 - Where this system exists in the real world
You interact with this design every day.
Stripe / Razorpay / PayPal payment gateways
E-commerce checkout payment processing
Subscription billing payment infrastructure
03 - What you'll master
Solve this once. Know it forever.
Guarantee idempotent payment processing
Model a payment state machine with retries
Design secure, PCI-conscious data handling
04 - What you'll design
8 functional · 4 non-functional requirements.
Accept card payments (credit, debit, prepaid)
7 more requirements inside
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05 - Companies that ask this
You may face this exact question in your next interview.
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