Thank you for your prompt reply. I'll take care of this query for you.
I've checked for any open investigations for the CSV upload process and found none. With regards to the name of the columns you have for the CSV file, it shouldn't matter since the system will still ask you to map them out. Say, for example, your Memo field can be mapped to the Description column in QuickBooks Online (QBO).
My colleague @FritzF shared an article above that shows 2 CSV formats accepted by QBO, which are 3 or 4 columns. Either format works fine.
Since an unusual error message keeps showing up, I suggest going through these steps:
Have other questions in mind? Place them in the comments below, and I'll get back to you.