Common Errors in QB Online Sync

Authentication Error
Reconnect with your QuickBooks Online Account.
First go to the Integration Setup page, expand Advanced Options at the bottom, check "Disconnect from QuickBooks Online" checkbox. Then connect to the QuickBooks Online again.

Amount calculation incorrect in the request. Amount is not equal to UnitPrice * Qty
This error is caused by one or more order that contains multiple quantity of an item. If that item subtotal price is not dividable by the quantity of the item in the order, QuickBooks Online will give this error.
Unfortunately QuickBooks does not provide the order id in the error message, so you will need to go to the Unexported Orders page, click on the "ready to export" filter on the top. Then check each order, and change the item subtotal to make sure it is dividable by the quantity.
If there are too many orders on Unexported Orders page, you can set the Export Order Start From and To Date on the Integration Setup page to reduce the date range and sync orders gradually to QuickBooks Online.