Hello there, confusedbusiness,
That's weird, let's edit your .CSV file into a 4-column template. Instead of negative amounts for expenses, please edit your .CSV file and add columns Debit and Credit.
Here's an example:
If the error persists, I recommend contacting our QBSE Support to isolate the issue. You can reach us here: https://help.quickbooks.intuit.com/en_CA/contact?product=qbse.
Please let me know if there's anything else I can be of help.