brevetto

@lorenzobros
Not sure if this helps any, but here is my structure:
Categories
Posts

@lorenzobros
In the admin >appearance > customize > options >slider if you don’t actually get a dropdown of categories, then it won’t work. Can you confirm that you have multiple categories to choose from in the admin?

Like this: Screenshot

@blatze
I had the same thing happen.
To fix I created a post under a different category. Went back to Admin Area -> Appearance -> Customize -> Dazzling Options -> Slider options and selected the correct category with the dropdown. If you only have one category it won’t work.

Hope that works for you.