Creating Debit and Credit memo with reference to billing document

Hi all,

Its Urgent..!

I need to create debit and credit memo through coding, i am using BAPI_BUSPROCESSND_CREATEMULTI to create order.

i need to create debit and credit memo with reference to billing document but i am not able to pass reference billing document number,

I tried  passing reference billing document in doc_flow with following values.

  ls_document_flow-ref_kind = 'A'.
  ls_document_flow-objkey_b =  vbeln.  " billing doc
  ls_document_flow-objtype_b = 'VBRK'.
  ls_document_flow-vona_kind = 'A'.
  APPEND ls_document_flow TO lt_document_flow.

  la_so_header-document_flow = lt_document_flow.

please suggest me how to pass reference billing document number..

Thanks,

Priyanka