Sure, but there’s no reason or value in a standard “idempotency-key”. The API would simply have a requestId, or depositId or whatever, and place it in the head

Sure, but there’s no reason or value in a standard “idempotency-key”. The API would simply have a requestId, or depositId or whatever, and place it in the header or body or whatever makes sense to the API. > This is an error checking facility to make sure that the idempotency keys are being used correctly. How circular. Idempotency keys are useful to make sure we’re using idempotency keys correctly.