Hi Sunil,
This field is QMNAM field of Notification.
See the Notification integration part to your Order.
If it is the case then 2 possibilities.
1. Code written User-Exit QQMA0014 is forcing this field to be filled.
2. Req radio button selected in the OIAL spro configuration against field VIQMEL-QMNAM (picture)
Please check these.
Jogeswara Rao K