Field Dependencies Category \ Subcategory

I wanted to create a Dependency for either Category or Subcategory and I am unable to use either as there is no checkbox to do so. FOr example let's say I have a category of IT Equipment and a subcategory of Loaner Laptop. When the user selects both of those dependencies I want the custom form I created to show up for them to fill out. I feel I may be missing something any assistance would be appreciated. 

The image below shows an example I can not select a subcategory however I am able to select Old User department.

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