I think there is a bug with the addon,
The link on the no-permission page seems to be broken....
it should point to "account/upgrades" page but instead it is linked as "account/upgrade" (Yes, its without the last letter S) therefore throwing a 404 page error to end user.
probably a simple typo...
Hi, I can see that you have updated your site to XF 2.2.1 :D. Any plans regarding this addon? Until to this date no one has been able to make similar or the same features from this addon.
Font Awesome 6 is based on CSS Styles, so I would say it doesn't matter whatever version of Xenforo or any other script you would use as ypu need to manually link FA6 in your themes.
I would recommend getting themes from ThemeHouse though as they know what they're doing and FA is fully supported.