method IF_EX_ME_PROCESS_PO_CUST~CHECK.
 
  CONSTANTS: c_parvw   TYPE PARVW VALUE 'ZM'.

  DATA:
    ls_header      TYPE MEPOHEADER,
    lt_partners     TYPE MMPUR_PARTNER_ALL_TAB,
    ls_partner      LIKE LINE OF lt_partners,
    lo_po_doc     TYPE REF TO IF_PURCHASING_DOCUMENT.
 
  ls_header = im_header->get_data( ).  " header details

  lo_po_doc ?= im_header.  " casting to purchase document

  lt_partners = lo_po_doc->get_partners( ).

  LOOP AT lt_partners INTO ls_partner WHERE data-parvw = c_parvw.
    EXIT.
  ENDLOOP.
  IF ( syst-subrc <> 0 ).
    MESSAGE.
    ch_failed = 'X'.
  ENDIF.