Hello there, Adavis-asea.
You'll encounter that message if you upload a file with an incorrect format. These are the file formats QuickBooks Online supports:
Let's make sure you're using the correct format so you can import bank transactions successfully. For more information, check this article: How to upload more than 90 days of bank transactions.
Don't hesitate to visit us if you have other questions.
Thank you for the reply. I've tried both OFX and CSV files and I get the same error. I neglected to included this before in my message. I've also checked both files for odd date formats as this has happened before and neither have them.
Of course. Perhaps if you deleted all but one transaction of the .csv file, and send that file through, this would be sufficient for me to troubleshoot. Don't want to push, we respect your privacy of course. If you wanted a better avenue to discuss, the support team are pretty good at fixing problems like this: https://help.quickbooks.intuit.com/en_AU/contact