You can follow the instructions for adding the fontawesome latest version to your app (at fontawesome).
In more recent versions of font awesome (as well as the pro version) there are other prefixes you can use instead of fa:. If you do include a different version of font awesome you can use prefixes such as fab: etc. You’ll find the prefix from the font awesome directory and clicking the icon you want.
(these should just work, though you won’t see the icons in the dropdown)