If your customer has outstanding balances, but their invoices are showing it is $0.00, it could be because their invoices have not been sent or at least marked sent or because there is a box checked to prevent invoices from showing an outstanding balance.

To check the sent status of the invoices, you will click the "Finance Tab" and click "Invoices."

Search for the invoices by customer or invoice number.

You can check the sent status here:

If the status is "Not Sent" and you want to send, you will select the box beside the invoice you wish to mark sent, click "mark as," and select how it was sent.

The outstanding balance should automatically update with any totals not paid from the sent invoices.

(Unless the box to "hide outstanding balances" is selected in your settings)

To check the settings, click the gear icon on the top right of the page and then the "Invoices, Estimates, and Receipts" Tab and scroll down. You will see these settings: