I know I used to have a macro to /tar something, then /cast a spell. And just had to roll the mousewheel to run the macro.
But I just tried to do it, and when I try and bind the key, I go into “keybind” mode and when I roll the mousewheel… nothing happens.
Did they break this?? Or am I just doing something wrong?
You need to put the macro on an action bar, then left click that button in the keybinds menu to put it in assignment mode, then scroll down.
ahhh! There is the subtlety!
I, of course, DID have it on the action bar.
The trick is that I just had it on some rando slot.
It has to be on a predetermined slot. Like 1, 2, 3, etc.
I was using all the number keys, but the “=” key was still open. Once I put it on that, it worked as I expected it/ as you just described it.
Thank you!!! 
(said another way: You can’t just bind “mouse wheel” to a random slot. “Mouse wheel” has to be assigned to an EXISTING KEY eg: 1, 2, 3, 4, =, etc)
edit: ahhhhhhhh and NOW I see it all…
The real issue is I was on “bar1” in the options menu, but I put my macro on “bar3.” Once you go into the options for “bar3” … it’ll work.
I learned a lot in this process, ty! lol