Cumulative Outstanding Balance on Supplier AC

I don’t know if I am missing something, but I cannot get a regularly used Supplier Account (which changes monthly) to show what we still owe that Supplier, & NOT mark partially paid invoices as Paid in Full. I have tried everything I can think of - not assigning a payment to any invoice, assigning a payment to an old invoice, & leaving the payment simply in the Suspense AC. Nothing I do permits a cumulative balance to give the remaining outstanding balance after Payments on Account. I am so frustrated because if I didn’t keep a spreadsheet, I would not know what our current outstanding balance is - WHAT do I need to do to achieve this - or is looking at filtered Purchase Invoices the wrong place to find the cumulative balance? If so, where should I be looking - am I being thick? If so, please enlighten me!

Go to Reports and select under Accounts Payable - Aged Payables or Supplier Statements.
They should give you what you are looking for.