Unable to import Inv. b/c Sales Tax is setup. One wrong entry posted to sales tax has been reversed. Due to that QBO is not allowing me to turn it off to import Inv.

Thank you for posting your concern in the Community, @cari2.

As of this time, the option to import your invoices with sales tax turned on, is unavailable in QuickBooks Online (QBO). This is why turning it off triggers an error. Rest assured that our development engineers are still working to make this function available to our customers. 

In the meantime, you'll want to consider visiting the QuickBooks App Center and look for a third-party app that allows you to import invoices with sales taxes into QBO. Alternatively, you can follow these steps in searching for one within QBO:

1. On the left side menu, select Apps
2. Click the Find Apps tab.
3. Look for an app on the search bar.

For your future reference, check out this article about personalizing the look and information of your sales forms: Customize invoices, estimates, and sales receipts in QuickBooks Online.

I'll be on the lookout in the comment section if you have more invoice and QuickBooks-related concerns. Stay safe.