Asset PO not throwing "Internal Order Budget Exceeded error"

[Shree78]

Hi Experts,

I have one scenario for my client that they need to restrict the purchase order if internal order budget exceeded error message should thrown

Eg: If allocated Internal Order value is Rs.1000 and i have assigned to Asset master.  Then if i raise the purchase order with account assignment category A and the purchase order value as Rs.1200.

System is allowing to process the purchase order.

but my client required error "internal order budget exceeded"  

It is high priority issue so please help me