"Error Importing. Darn. File upload failed. (Probably our fault.) Please give it another try. If you see this message again, you might need to contact us."

Try opening your QBSE account on any private/incognito browser. If the same error persists, you can use one of the converter tools (e.g csv2qbo @ $60 one time license) as a workaround.

https://www.moneythumb.com/?ref=110

Thanks for sharing your concern, @rasid.pac. I have some insights to help you import .csv files into your QuickBooks Self-Employed account smoothly.

To ensure successful uploading of your CSV file, it's essential to make sure that all details are in the correct format. 

We can create three or four-column layouts of a CSV file for your data. You can refer to this article to be more guided about the file format: Format CSV files in excel to get bank transactions into QuickBooks. It also includes detailed information on modifying them in case you receive an error message when uploading. 
 

Moreover, I'm adding this reference to guide you in reviewing and organizing your income and expenses: Categorize transactions in QuickBooks Self-Employed. It includes additional steps on how to create and manage category rules.

You can always get back into this thread if you have additional queries about importing transactions in QBSE. We'd be delighted to assist you again. Keep safe and have a good one!