Start by updating your Accounting Categories

Under the Accounting Category, for the ticket items, the Inventory Will Not (Be) Be Maintained.  

You may not be able to change this setting unless all of the items that point to this Accounting Category have zero inventory.

Find all products in the above Accounting Category:

The easiest method is to go to each item and manually zero out the current onhand quantity (both positive and negative) for each item.  Once that’s done, then you can change the Accounting Category to Inventory Will Not (Be) Be Maintained.