XF 2.1 Random font awesome icons not working

[Heraldic Age]

For example, this icon doesn't show up on my website when using Unicode: f15a in my style templates. Other icons work fine.

fa-btc: Font Awesome Icons

Font Awesome, the iconic font and CSS framework

fontawesome.com

What could cause this?

 

[Ozzy47]

Try using, fab fa-btc