# Idempotency

A `POST` made with a key accepts an `Idempotency-Key` header: any unique string per logical request, for example a UUID. Retrying with the same key and the same body within 24 hours replays the stored answer instead of running the request again, so a timeout never creates a second monitor. Replayed answers are 2xx, 400, 404 and 422. The same key with a different body answers 422; a retry while the first request is still running answers 409. Use a new key for every new request.