V15 How to display field in different tab in same doctype?

I want to show grand total and outstanding amount from sales invoice to payment tab.

IMO, there are 2 ways to achieve this:

  1. Create new field that show same value
  2. Move the field to payment tab

For 1st option, I don’t know the way to make it calculate instantly, so I believe it will be a client script since calculation should happen as soon as amount change even without saving the document. But I’m not a developer, so there will be a long way to learn just to achieve this.

For 2nd option, I don’t mind that field not showing in details tab, but I cannot move the field between tabs, and I cannot expand fields table in customize form, so I cannot drag the field to another fields set. It only shows 25 fields at a time, so I cannot move it from field number 30 to field number 60 where I want the field to be in form view.

How can I achieve this?