Error for Partner Function in BAPI_PO_CREATE1

[#1]

While testing BAPI_PO_CREATE1 in tcode SE37
we are facing error for PATNER FUNCTION as shown in the below snapshot,
but the same when done manually gets accepted and no errors pop-up,
How to resolve this error, as we need to use the BAPI for interface.

[RaymondGiuseppi]

Did you ensure the correct format of PARTNERDESC (consistent with LANGU) when populating POPARTNER in BAPI_PO_CREATE1?