RE: Netting invoices and payments to $0 on AR aging
In addition to Debbie's suggestion, it's possible that your apply dates are later than you transaction dates. For example, if you applied them yesterday the system would have defaulted the apply dates to 3/12/2021. Most people that don't do this every day forget to change the apply dates, or don't even know they can. If you're printing a historical aged trial balance as of 2/28/2021, those transactions will show as unapplied, because they were truly unapplied on 2/28.
If you drill down on the Amount Remaining for either the payment or the invoice in GP you can see the Apply Date. Note this is the Document Apply Date, there is also a GL Apply Date - that is stored in tables and I don't think you can see it anywhere in the GP user interface. This is important because if you are printing your historical aged trial balance using the GL Posting Dates, it will use the GL Apply Dates.
You can change the apply dates when you're applying transactions and if they're already applied with an "incorrect" date you can unapply and re-apply with new dates.
<em>-Victoria</em>