@PitaJ The forum is running version v1.10.1.
However, neither the chat function nor the group mention function are working. Anything else I could try to make it work please?
In NodeBB, subcategories are referred to as child categories. In order to set up your subforum, you would create your necessary categories (one for mobile phones, and then others for android, ios, etc) and then set the parent category of your intended subforums to be your mobile phones category.