Hello Priyesh,
The flag that you set doen't really works as per the SAP function module documantation.
Try to do following stpes :
- Create one more table of the same type,(say itab2)
that contains your data to be downloaded.
- Append/Insert your header information that you need to be displayed at the begining.
Fill itab with the header.
- Do as follow to append your previous table to new one.
APPEND LINES OF itab1 TO itab2.
- Now do pass itab2 to the FM, it will surely work.
Reward if helpful.