hard20 pts · first answer countsapi-designreliability

Preventing double charges on retry

The checkout page sends POST /api/payments. The request times out on a slow network, the client retries, and the customer is charged twice. What is the most robust fix?

A.Disable the Pay button for 2 seconds after a clickB.Increase the server timeout to 60 secondsC.Send a client-generated idempotency key; the server stores it with a unique constraint and returns the saved result for any repeat with the same keyD.Change the endpoint from POST to GET

Two buyers, one item left →