Before using the QuickBooks Online integration, you'll need to ensure the following Accounts exist, Sales of Product Income, Cost of Goods Sold, Inventory Asset, Discounts Given, and Customer Deposits.
In addition, if you collect Sales Tax, you'll need to have ONLY one Tax Code.
Instructions are below on creating Accounts and a TaxCode.
Go to the Accounting tab
Go to the Chart of Accounts tab
Click the New button
For each of the missing Accounts, create based on images below.
Sales of Product Income
Cost of Goods Sold
Go to the Taxes tab
Click the "Add/edit tax rates and agencies" link
If a TaxCode exists, you are done. Otherwise, click the New button
Enter the Tax name, Agency name, and Rate