> If there is an attempt to reuse an idempotency key with a different request payload, the resource server MUST reply with a HTTP "422" MUST seems too strong h

> If there is an attempt to reuse an idempotency key with a different request payload, the resource server MUST reply with a HTTP "422" MUST seems too strong here to me. For some applications it's probably sufficient to treat this case the same as if the payload was the same, and it requires the server to persist either the original payload, or a hash thereof. And what if the payloads differ only by a timestamp, or a randomly generated id, etc.?