Font Awesome icons not working

[XFFA.IR Bot]

The older <i> method does not work. I've tried using the <xf:fa> and that doesn't work either. For example, this produces nothing:
Code:

<xf:fa icon="fas fa-yin-yang"></xf:fa>

The above is used in a custom BB code:
Code:

<xf:fa icon="fas fa-{text}" />