Hello, TBSParkin2011.

I can understand you want to have a simple fix to your concern. However, as mention by my peer, you'll need to create a  bad debt and then create a Credit Memo to put the unpaid portion to the Expense account to record a negative sales tax.

I've added this article for additional information in creating a credit memo: Give your customer a credit or refund in QuickBooks Desktop for Windows.

For future reference, read through this article to learn more about how to record an invoice payment.

Don't hesitate to leave your questions or clarifications about the sales tax liability report. I'll get back to you as soon as I can.