Hi Aslam
You can create Enhancement Spot for this change at inculde MV10AF0M_MV10A-KDMAT.
1, you need to show implicit enhancement options.
2, create the enhancment spot in the form MV10A-KDMAT. create at beginning of it.
3, in this enhancement, you can add the logic to check if the field KDMAT is space. send the message.
Regards,
Yawa