During Invalidate and Edit operation: Order based invoice with multiple lines – to see what is the total amount of lines?

Meaning: I have an expense invoice which I need to change to Order based with 5 PO lines.
Each one has different quantities and unit prices and while creating these lines we are not sure if total of lines are same as our invoice total:

If Medius would add a SUM field below or anywhere in Amount box, it would be huge help during Invalidate & Edit as we can have up to mentioned 999 PO lines and if our totals do not match, we must invalidate again and again.