Schema Error: Products Do Not Have Categories
In order to produce search and shopping Campaigns, every product in your inventory must be categorised.
If any of your products do not have categories, you will get an error on the Inventory screen under Schema Errors. These products will not appear in your search or shopping campaigns.
To correct this problem, you should update your website to put all of your products in at least a first category. How you do this will be different depending on your website platform