Middle Mouse Button Not Recognized

Hello. I am trying to bind the grenade throw 'G' to my middle mouse button (scrolling wheel). I have selected the mouse button assignment column on the right but when I click the middle button it does not recognize it. I have always used this for grenade throwing. The side buttons are recognized just fine.

I use a Corsair harpoon mouse. I also tried mapping it through iCue software but no luck. Anyone else have this issue? Any advice is appreciated!