OK. Since I don’t have that device I am stuck trying different things and hoping they work. So before I go changing code around, I want to ensure you typed those exactly as shown here. Capitals and everything.
If that is a solid “yes, that’s what I did”, then I’ll try something else. I have a couple of ideas, and what I can do is make the volume up, down and mute all act slightly different, then get you to add the exact same intent for all three, and let me know if any of them work.