Process Constraints issue in Order management

Hi,

I was developed a custom procedure as per my below requirement.

if the order line unit selling price changed to unit list price, i need to send notification to the list of users and applying a custom hole.

i developed the logic and attached to the process constraints template. 

It's calling my procedure . my issues is  it's firing the process constraint procedure before saving the record in Order screen.

how can i call my process constraint logic after user saved the record?

in process constraint screen i am defined as below

Operation --> update

Attribute --> unit selling price