Thanks for dropping by the Community today, I'm happy to help. More than likely the reason for the discrepancy between your a/r aging report and the open balance is because the a/r aging report only shows past due invoices. I would suggest checking to see if the invoices are past due. If not, that is why your customer balance is higher than your a/r aging. I'm including a link below that goes over how to run an accounts receivable aging report and everything you need to know about them.
Here, I'm also attaching a link to our support team if you'd like 1-on-1 guidance to walk you through the process. If you have any other questions, feel free to post here anytime, any day. Thanks again and have a lovely afternoon.