Can I use a custom lot number during WIP Completion?

We have a requirement where WIP completions are received from an external system. We are using the Work Order (WO) number as the lot number, and this has been configured in the Plant Parameters. However, we are also receiving a custom lot number from the WIP completion process. When I attempt to update the Complete Work Order with the custom lot number, I encounter the following error. Could you please suggest a solution for this issue?