Hallo,
ein Coding das funktioniert:
* Fill order_header_in
order_header_in-doc_type = 'TA'.
* Fill order_items_in
wa_order_items_in-material = '000000000000000001'.
wa_order_items_in-req_qty = '1000'.
APPEND wa_order_items_in TO order_items_in.
* Fill order_items_in
wa_order_partners-partn_role = 'AG'.
wa_order_partners-partn_numb = '0000000001'.
APPEND wa_order_partners TO order_partners.
* Execute Function Module BAPI_SALESORDER_SIMULATE
CALL FUNCTION 'BAPI_SALESORDER_SIMULATE'
  EXPORTING
    order_header_in           = order_header_in
  IMPORTING
    return                    = return
  TABLES
    order_items_in            = order_items_in
    order_partners            = order_partners
    order_items_out           = order_items_out.
 
Gruß
Wolfgang