Hi, @contact191. Welcome to the Community!
When your CSV file contains a 3-column layout, make sure to choose the right format when importing.
To begin with, when choosing the 3-column layout during the import process, you have to choose the One column option and make sure that the date format matches the date in your CSV. Also, verify your columns are in the correct order (Date, Description, Amount) and ensure there are no extra spaces or hidden columns.

If you're still seeing the same error message, you can clear your cache and Intuit-specific cookies to remove outdated or corrupted data that causes the issue. You can also use another supported browser as an alternative option.
Once you import your transactions successfully, you can now categorise your transactions in QuickBooks Online.
If there's anything else you need help with, you can always return to this thread.