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Payment API Design & Integration
Section 3 of 9
Idempotency patterns, authorization/capture state machines, webhook delivery architecture, Stripe/Adyen SDK integration, FX handling, and reconciliation systems
4 hours•advanced
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Key Takeaways
- •Idempotency keys are the single most important pattern in payment APIs — every mutating operation must accept and honour them
- •Authorization and capture are separate steps — a captured amount cannot exceed the authorized amount
- •Webhooks need HMAC signature verification, idempotent handlers, and exponential backoff retry
- •Money arithmetic must use integer minor units (cents/pence) — never floats
- •Reconciliation is an engineering system, not an accountant's spreadsheet — build it from day one
📝Personal Notes
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