In the context of API requests, idempotency is a property which guarantees that the result of performing an operation on a resource is always the same, regardless of how many times the operation is performed. This prevents unintentional duplicate requests.
To prevent duplicate payment requests, the Checkout.com API's /payments endpoint supports idempotency.
To perform an idempotent request, provide a unique key in the request's Cko-Idempotency-Key HTTP header.
For more information, see Idempotency.