Thanks for the additional details, @forestschool.

I'll outline a couple of handy information to help you import the IIF files seamlessly.

QuickBooks Desktop (QBDT) gives you the option to review and resolve the errors found in your .IIF file. Thus, you're getting the said prompt you've stated above.

Here's how to review the errors:

1. Click the Review now button.
   
2. Find the ERROR to see what the problem(s) with the file is.
3. Correct the errors as needed and then click Save. 
4. Select Yes if you want to keep the file type, and then close the File not imported window.
5. Import the new, corrected file as you normally would.

I'll be adding this helpful link for more details: Resolve IIF Import in QBDT 2019 and later.

Also, I recommend using the IIF Import Kit. Then, compare the header, and other data fields with the ones on your file. This can help spot any formatting issues that lead to the error message. 

Additionally, QuickBooks doesn't offer technical support for IIF file import. You can contact Stripe's technical support directly for assistance. Otherwise, you'll need to seek further help from an IT guy to import the file successfully.

Lastly, you can perform other tasks with your IIF files, such as bulk editing them, etc. Please head to this article for more insights: Tasks you can do with IIF files.

Feel free to tap me any time for other questions you may have with IIF files. I'm here to answer them for you.