HardFintech45 min

Design a Payment System

Design a payment system like Stripe or PayPal that handles transactions, supports multiple payment methods, and ensures financial consistency.

StripePayPalSquareAmazon

Functional Requirements

Process credit card, debit card, and bank transfer payments
Handle refunds and chargebacks
Exactly-once payment processing (no double charges)
PCI DSS compliance for card data
Multi-currency support

Steps (0/6)

Step 1: Clarify Requirements

Scale: 1M transactions/day. Payment methods: cards, bank transfers, digital wallets. Features: pay-in, pay-out, refunds. Consistency is critical: no double charges, no lost payments. What about recurring payments?

Key Points

1M transactions/day → ~12 TPS average, 100+ TPS peak
Consistency > availability for financial systems
Must handle partial failures gracefully
PCI DSS compliance is mandatory for card data

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