I can help you on how to successfully import invoices in QuickBooks Online (QBO), @royalmedicaltran.

Currently, importing invoices will only be successful if you are not using the Sales Tax Center (sales tax codes) yet. Thus, we encounter the error if the feature is already turned on.

There are 3 ways to get your invoices saved/recorded in your QBO account. You can either:

• Record invoice manually.
• Use third-party application.
• Use batch transaction on QBO Advanced.

Meanwhile, here's how to enter the invoices manually one at a time:

1. Click the +New button at the upper left part of the screen.

2. Choose Invoice option under customers.
 
3. Fill in the necessary details:

Add customer
Invoice date
Due date
Product and Services

4. Select Save and close.

To look for a 3rd party app that is suitable for your needs You can go to Apps Center/menu: QuickBooks App Store.

The Batch function to create bulk invoices that's available in QBO Advanced. You can upgrade your subscription to it if needed. 

If you still have questions about importing invoices, please feel free to leave a message and you'll be assisted directly.