how do I use the font awesome class what do I put in the box this <i class="fa-regular fa-eyes"></i> that doesn't show could you please point me into the right direction or show me what to enter in the Font Awesome Icon Class.

If this is in relation to a resource from the Marketplace, you'd be best posting in the support topic for the resource itself.

If this is in relation to the base Invision Community software then you can't use 'fa-regular' as IC only supports FA 4.7 icons, not FA 6 (which I believe is where fa-regular was added)