Backend · Senior · Theory

A client calls your create-payment endpoint, the response is lost to a timeout, and the client retries the request. How would you design the API so the money isn't charged twice?

~4 min by voice

How to approach it

This checks whether you can make a non-idempotent operation (a POST that creates a payment) safe to retry: an idempotency key from the client, atomic recording on the server, correct handling of races, and idempotency along the whole chain, including the external provider.

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api design idempotency

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Answer by voice

The interviewer will ask this question and listen. Think out loud and ask for a hint if you need one. When you're done, pause or tap “That's my answer”. In about a minute, your score and the points you covered show up here.

Best with headphones · ~4 min