Hi @shawn-lotusluxur,

I've got the steps you need to take to mark a paid invoice in QuickBooks Self-Employed (QBSE), as unpaid.

Here's how:

1. Go to the Invoices tab.
2. Locate the invoice in question.
3. Click the View drop-down menu.
4. Choose Mark as unpaid.

Check out the screenshot below for your reference: 

In case you need to track sales tax in QBSE by hand, take a look at this article: Manually track sales tax in QuickBooks Self-Employed. 

Do you have other questions about invoices in QBSE? Place it in the comments below, and I'll take care of them for you.