How to run script after clicking Fill% Button in Invoice (Progress Billing /Invoice in Netsuite)

Hello,

So Netsuite has this progressive billing in invoice where if I click the Fill% button, a pop up window will show and in there, I can enter the % of how much we are billing for this Invoice.

Now, we have a script that we want to run after Fill % is clicked and processed changing the total amount. I tried Client script, all the available functions there but it seems nothing is getting triggered even the fieldchanged and post sourcing function. (When fill% button is clicked, and you enter for example 50%, the total amount will changed so by theory the client script(fieldchanged) that we have should be triggered) but currently nothing is getting triggered after the fill% button is clicked and do the process of updating the amount.