"Error during modification. Specified parent item is inactive. Inactive items cannot have active childs".
This error message could be related to the way Product Classes have been set up.
Please log in to your Revel URL and go to Products > Classes.
Click the pencil icon in each product class' row and check that each Product Class has a Parent Class attached.
If there is no parent class attached, you will see the 'Parent' field as blank (like below).
If they do not, please enable a parent class for every product class and save.
For more information on Product Classes in Revel and on how to assign a parent class to a product class, please read here - Product Class Guide.
Make sure to re-open your QBPOS App and your QuickBooks Desktop Company and wait for the sync to happen again (please note - this may take up to an hour).
If the issue persists, please call Revel Support.