VAT Tax is an abbreviation for Value Added Tax, it is used for sales, service or similar taxes. Ensuring this is set up correctly will allow accurate records of taxes collected.
If the taxes are not set up correctly you will receive the following error.
nullA business validation error has occurred while processing your request : Business Validation Error: Make sure all your transactions have a VAT rate before you save. This means you will need to add a tax rate to the Taxes that you already created in QuickBooks.
To correct the error any taxes created in QuickBooks needs to have an assigned tax rate value even if it is zero.
See links below for further guidance.
Set up Your Sales Tax - QuickBooks Community: