BAPI_PO_CHANGE to change Gr-Bsd IV

Hi,

I have a problem when I use  BAPI_PO_CHANGE to set Gr-Bsg IV for received items.

This is my code :

CALL FUNCTION 'BAPI_PO_CHANGE'

   EXPORTING

    purchaseorder                =  s_ekpo-ebeln

*   poheader                     =  t_bapi_poheader

*   POHEADERX                    =  t_bapi_poheaderx

*   NO_AUTHORITY                 =  'X'

  TABLES

    return                       = t_return

    poitem                       = t_poitem

    poitemx                      = t_poitemx

.

Please heeelp ?: