Need to customize pay group in Manage Installments screen

Summary

Need to customize pay group in Manage Installments screen

Content

Hi All,

We have a requirement where in we need to make a couple of fields to be set to read only and Pay group to be customized to have it as a required field in Manage installment screen which is accessed via Invoice actions. After enabling sandbox and going into invoice screen, Once we click edit pages and open up the manage installments screen from Invoice action, we are unable to customize the screen. The window is like a Modal window which freezes the background screen.

So our ask