I enjoy using the hyperkey functionality (within the BTT app) for opening websites or apps.
However, when I try to assign it to a system functionality, such as volume up/down, or keyboard brightness up/down, it does not work. I assigned a popup to show up every time the shortcut is triggered, and the popup DOES trigger every time, but the functionality itself (volume or brightness) does not work.
I'm running the latest version of BTT.
unfortunately I don't think there is a workaround for this at the moment.
The volume and brightness keys that BTT emulates don't work if option is pressed and due to the hyperkey thing BTT can not release that modifier before sending the brightness / volume keys
I appreciate your response, and this does solve the mystery (even if something doesn't work, it's still good to know WHY it doesn't so that I'll stop myself from endlessly trying to troubleshoot it).
What's strange is that if you 'manually' press shift+control+option+command+volume up, then the volume up works normally, despite the option key being pressed. What am I missing here?
Ah, in your case the arrow up key adds an implicit FN key modifier. Without that it would indeed work as shift seems to cancel out the option issue. However with the arrow key it's like pressing shift+control+option+command+FN+volume up
Maybe it will work when using some non-arrow key
I've tested it out with a non-arrow key:
if I set Shift+Control+Option+Command + U to 'Keyboard Illumination Up', it DOES work when triggered 'manually', but DOES NOT work with the use of a hyperkey. 
Volume up/down and brightness up/down works, but with some quirks when it comes to full/small steps). I suppose that can indeed be explained by the hyperkey utilizing the 'option' button.
But any idea why keyboard illumination refuses to work?
