QuickBooks: Transaction Amount Must be Positive

When posting an invoice from OnTime to QuickBooks, you may receive the following error message:
There was an error when saving a Invoice. QuickBooks error message: Transaction amount must be positive.
This message may appear when posting an invoice where the total is a negative amount. QuickBooks does not support invoices with a total of less than zero. To resolve the issue, check the invoice within OnTime and ensure that all orders posting to OnTime have a non-negative total amount.