SeniorSenior (6–10 yrs)System DesignStripePayPalAmazon
Idempotency keys
How do idempotency keys protect payment APIs?
Answers use simple, clear English.
Quick interview answer
Clients send a unique key per logical operation. Server stores key→result; retries with the same key return the original result instead of charging twice. Combine with upserts and exactly-once side-effect design where possible.
Detailed answer
Clients send a unique key per logical operation. Server stores key→result; retries with the same key return the original result instead of charging twice. Combine with upserts and exactly-once side-effect design where possible.
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