Problem
Some customers have a total of $0 in the AR Transactions By Customer report, even though there are outstanding invoices over 121 days. This is due to the Exclude net $0 balance invoices filter being enabled or the customer having already paid the amount due within the last 120 days.
Solution
Disable Exclude net $0 balance invoices filter.
Go to the navigation bar and click Reports.
From the side menu, click All Reports and click AR Transactions By Customer.
Review the Exclude net $0 balance invoices filter. It should be checked.
Click Exclude net $0 balance invoices filter to uncheck it.

Run the report again by clicking Run Report.
After following these steps, you should see the correct totals for each customer. If a customer's total still shows as $0, it means the customer has paid the amount due within the last 120 days. For more, see AR Transactions By Customer report.