# Idempotency In Zūm APIs, idempotence means that requests that have been previously processed successfully are not reprocessed again. The response for the completed processing is reported instead. All `POST` requests accept idempotence keys. Sending idempotence keys in `GET` and `DELETE` requests will have no effect, as these type of requests are idempotent by definition. To submit a request with idempotent processing, add the key `idempotency-key` in the header. The value for this key should be a unique identifier for the message with a maximum of 36 characters (we recommend a UUID). If you don't receive a response (for example, in case of a timeout), you can safely retry the request with the same header. If we have already processed the request, the response to the first attempt will be returned without duplicating the request in our database. Idempotence keys are persisted in Zūm Rails side for 1 hour, which means if you send the same key after 1 hour, the request will be handled as a new request. If the same idempotence key is used on two different transactions within 1 hour of each other, the second transaction will not be created. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.zumrails.com/api-reference/idempotency.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.