Qty/cost center in ML81N

Hi All,

I have created service PO for 10QTY (5 for cost center 1 and 5 for cost center 2) and now when I go to service entry sheet (ML81N) I am able to post all the 10 QTY to cost center 1 but we dont want like this we want system to show error message if the qty exceeds per cost center.

How to configure this.Please advise.

Thanks in advance

Pavan