As mentioned here, if you're using ligatures to render the Font Awesome 5 icons, these won't render in the browser output. You can only copy & paste the icons from the FA cheatsheet or use our widget library to drag & drop the icons into the editor.
If you're unable to render the Font Awesome 4.7 icons either, could you make sure that its CSS link is included in the Web Fonts tab of the Generate HTML settings? If you could also share the .rp file where this isn't working for you, I'll be happy to take a closer look. Thanks!