What do you call what remains to be paid of invoice?
There is an invoice in a computer system. It has the "total sum" and the "paid sum" associated with it. How do you call "what remains yet to be paid" on this one invoice? And which sign, plus or minus should be displayed along this number?
The term (in the US, at least) is balance due.
No sign needs to be displayed, since balance due expresses that money is owed by the customer. If you owed the customer, there would be a credit.
https://financial-dictionary.thefreedictionary.com/balance+due