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Design a Payment Processing System is a hard system design interview question covering Distributed Systems, Databases, payments, idempotency — the kind asked at FAANG (Facebook/Meta, Apple, Amazon, Netflix, Google) and AI-first companies like Anthropic, OpenAI, and Nvidia.
Design an internal payment service that orchestrates external payment providers such as Stripe and Adyen. It must support cards plus regional methods (UPI, iDEAL, Pix), 30+ currencies, refunds, and chargebacks. A double charge or a lost payment is unacceptable.
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