Key property does not have an output mapping in query operation

Hi Experts,

We are trying to create an Odata service for retrieving the PO list through RFC BAPI_PO_GET_LIST.But when implementing the GetEntitySet(Query) encountering an issue "Key Property does not have an output parameter in query operation" when we try to create "Propose Mapping".

Kindly suggest.Thanks in advance.

Thanks & Regards,

Sravanthi.