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Idempotency, retries & failure handlingEasySDE-1

A user taps 'Pay' twice on a slow 3G connection and gets charged twice. What is idempotency, and how would you change the payment API so this cannot happen?

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PaytmPhonePeRazorpayStripe

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Answer out loud as you would in the room — clarify, give numbers, name the trade-off — then compare with the model answer.

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Design a payment system (Stripe-like) Lesson: Designing the API

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