Thanks for contacting our Community, @user76637.
I'd be glad to share with you the difference between these two VAT codes in QuickBooks Online (QBO).
OOS refers to the Out of Scope VAT code which is typically associated with QuickBooks Desktop and other countries for QBO products. Though, this code and the No VAT code are both the same.
You can designate these two for goods and services that are outside the scoop of VAT and not reported on the VAT return. This includes anything you:
In addition, you can add and Deactivate tax rates in QuickBooks. If you don't see them on your tax list, these instructions can help you create the ones you need: How do I set up sales GST/VAT rates and use them on forms?
Let me know if you have any other queries. I'll happy to answer them for you.