Allow me to share some insights about this error you're getting in QuickBooks Banking and how you an resolve it.
The mentioned error normally comes up when adding an online banking transaction that doesn't have a tax code in it. To avoid this from happening, make sure to input all necessary information to add bank entries successfully.
Another option to resolve this error is to create a counterpart transaction in QuickBooks then match it with the bank entry. Do that by going to the + New icon the choose the sales or expense transactions you can match in the Banking page.