XF86MonBrightnessUp/XF86MonBrightnessDown special keys not working

I'm trying to enable some multimedia keys, and the ones for volume do work. F5 and F6, the ones for increasing/decreasing do not work, I do not know why. When I run in the terminal: xbacklight +10 I can see the working effect. When I try my binded special keys (which are set to ~/.config/i3/config): # Sreen brightness controls bindsym XF86MonBrightnessUp exec xbacklight -inc 20 # increase screen brightness bindsym XF86MonBrightnessDown exec xbacklight -dec 20 # decrease screen brightness Obviously, the media keys must be combined with the fn key. However, I don't see the effect. Any solutions?