'Dynamic Bones' addon doesn't show up in "Add component"... (Same goes for all custom addons)

I'm currently trying to add the "Dynamic Bones" addon to my avatar, however the dropdown menu (as shown on linked attachment) returns nothing despite having imported both packages... Same results when trying to add any custom addon really...

Oh, and it's a VRChat model I'm working on-

Screenshots:

Components menu: https://media.discordapp.net/attachments/519174380404736000/954047749211422801/unknown.png

Assets tab https://media.discordapp.net/attachments/519174380404736000/954048253773643837/unknown.png

I tried creating a brand new project, running Unity on Administrator mode and even tried it with other models, but once again to no avail. (Yes, this does mean my Avatar/model isn't the culprit)