Thanks for providing your concern on this thread, @wbfinc.

Let me provide some insight into how progress invoicing works in QuickBooks Online (QBO).

Yes, you're correct that when using the progress invoicing feature, it won't reflect the unpaid balance on your next invoice if it is only a percentage of the total in a line item.

As a way around, you can pull up the created estimate instead to show the previous balance of your previous invoices. 

You can also check the remaining amount of your estimates by running the Estimates & Progress Invoicing Summary by Customer Reports. Let me show you how:

1. Go to the Reports menu.
2. In the search field, you can enter "Estimates & Progress Invoicing Summary by Customer".
3. Change the Report period it was created and then Run report.
   

You'll also want to personalize the format for your reports. Kindly refer to this article to learn more about the process: Customize reports in QuickBooks Online.

Additionally, you can personalize the appearance by adding specific info to your sales forms. Check out this article for more information: Customize invoices, estimates, and sales receipts.

Let me know in the comment section if you have further concerns regarding progress invoicing in QBO. I'll be more than happy to help. Have a nice day!