Hi there, @MDD2021.

Thanks for getting back here. I've got steps to further help you fix the error when importing your IIF files. Here's how:

1. Select the Review now button.
2. Find the ERROR to see what the problem(s) with the file is.
3. Correct the errors and then, Save.
4. Click Yes, if there's a prompt that says you want to keep the file type. 
5. Close the File not imported window.
6. Import the corrected .IIF file again. 

For more info about this process, please see this article: Improved IIF Import in QuickBooks 2019 and later.

However, if the issue persists, I highly recommend reaching out to our Technical Support team. This way they can have a formal investigation to determine what's preventing you to import the IIF file. You can also request a screen sharing session so they can check your setup. To do so, please follow these steps:

1. Click the Help menu and select QuickBooks Desktop Help.
2. Click Contact Us.
3. Enter your brief description of your concern. Example: Cannot import customer file using IIF files in QuickBooks Desktop. 
4. Select Continue.
5. Choose either Start messaging or Get a callback.

Then, to find articles you can bookmark for future use, check out our QuickBooks Desktop help articles site. Simply, enter a keyword of your concern on the search box or select any of the categories displayed.

Should you need any assistance with importing your IIF files in QuickBooks, please leave a reply below. I'm available here to help at any time. Take care always.