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← Square
Design a Payment Processing System
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558 — full content available
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category:
System Design
difficulty:
hard
freq:
high
first seen:
2026-01-14
[HARD]
[SYSTEM DESIGN]
[HIGH]
Payments
Distributed Systems
Security
Reliability
$
cat
problem.md
Design Square's payment processing pipeline.
Requirements:
Process credit/debit card transactions
Support multiple payment methods (cards, wallets, ACH)
Real-time authorization and capture
Handle settlements and reconciliation
Implement fraud detection
Maintain transaction history and receipts
Key Components:
Payment Gateway
: Entry point, validation, routing
Authorization Service
: Verify funds, fraud check
Ledger
: Double-entry accounting system
Settlement Engine
: Batch processing
Notification Service
: Receipts, alerts
Key Considerations:
Idempotency (prevent duplicate charges)
PCI-DSS compliance (data encryption)
High availability (99.99% uptime)
Low latency (<500ms for auth)
$
cat
sources.txt
▶
user@intervues:~/square$