QuickBooks Online couldn't work out the sales tax on a settlement, so it rejected it.
How to fix it
In QuickBooks Online, check that your sales tax settings are complete.
Find the QuickBooks customer the store uses. In ConnectBooks, go to Stores & Files and click the store. On the Accounting tab, under Accounting Settings, click Settings. The customer is in the Customer field on the QuickBooks tab. Some Amazon stores have an FBA Customer and an FBM Customer. If there are 2, check both.
In QuickBooks Online, open each of those customers and check that the address is complete.
In ConnectBooks, go to Accounting Export. Click the 3 dots on the settlement and choose "Resend to QuickBooks". If you see Settlement, COGS and Both, pick the one that shows the error.
Frequently asked questions
The settings and the address look fine.
Contact support and send us the settlement's CB ID#. It's in the CB ID# column on the Accounting Export page.