Did you pass the below EXPORTING parameters.
CALLFUNCTION'SD_SALESDOCUMENT_CHANGE'
EXPORTING
salesdocument = <fs_atp>-vbeln
order_header_in = gs_order_header_in
order_header_inx = gs_order_header_inx
simulation = ' '
business_object = 'BUS2032'
call_from_bapi = ct_charx
IMPORTING
sales_header_out = gs_sales_header_out
TABLES
return = gt_return
item_in = gt_item_in
item_inx = gt_item_inx
schedule_in = gt_schedule_in
schedule_inx = gt_schedule_inx
items_ex = gt_items_ex
schedule_ex = gt_schedule_ex.
Regards,
TP