Never mind. I found the error.
Wrong:
fas fa-windows
fas fa-apple
Right:
fab fa-windows
fab fa-apple
The instruction in the software is misleading:
Enter the name of any FontAwesome icon class, including the fas fa- prefix.
I have no experience with Font Awesome, but if I had to guess I would say that s in fas stands for symbol and b in fab stands for brand. I don't know how many classes there are, but these two seem to be most commonly used. Instructions could be handled differently though. Perhaps a link to internal resource on the topic rather than a link to Font Awesome website? It looks like there used to be a more simple command in older versions of Font Awesome, e.g. fa fa-apple.
