I think we need to go back to the start of this project and learn to crawl before you try to run.
Can you please re-explain the issue without refering to any code or work you had previously done. Lets start fresh so I can understand the issue.
* You have a CPT called ‘Promo Boxes’
* ‘Promo Boxes’ suports the ‘category’ taxonomy
* Promo Boxes has some custom fields. What are they? Are they relevant to this issue?
* You are tyring to load the category ID. Where from. What URL are you looking at? What template file is running?
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