I need help with macros.

So I've been trying to make a macro for awhile now and it hasn't been working. I make the macro, set the keybind then add what the macro will do, I'm trying to have it spam TAB as long as I have it pressed. When I go to set what keystroke the macro will do, I click on the little box where it shows what key it will press then I press my key and it doesn't do anything. The box stays blank and this happens with every key I try to use not just tab. (I'm on razer synapse 3 btw.)