FN+{F1-F12} keys not detected by xev

I was trying to bind my fn+f1-f12 keys (which I'm trying to use for volume controls and such) in sxhkd. Before when I used Linux, I bound XF86Audio* keys (e.g. XF86AudioLowerVolume) and it worked, and xev detected them. Now I switched to FreeBSD, xev does not detect any fn+f1-f12 keys at all, xev just outputs nothing at all when I press fn+f1-f12, and the sxhkd binds I used before don't work.

Is this a FreeBSD or X configuration problem? How can I get it to detect my fn+f1-f12 keys?

(Very sorry if there is a better section! I didn't see one, I didn't know which one to pick...)