It is easy for you, how to check outstanding student list of current invoice.
Go to Reports => Students Info => Students Fee balance 2
Change the Balance (Changeable) filter all to Balance = 0
Click Go button
If you want to see unpaid students of current invoice
Go to Reports => Students Info => Students Fee balance 2
Change the Received (Changeable) filter all to Received > 0
Click Go button
For more help you can see this video