I see there is an option to set up a round robin on a keymap, and in Mosg's manifesto, he mentions doing it with stuns/interrupts, but he never really explains how to do it.

If I have my stun spell set up on the "=" key ingame on both my characters, how would I go about setting up a keymap to use it in a round robin fashion?

I tried making a mapped key on my control keymap, sending the key to all windows, and clicking the 'round robin' check box, but the key never gets fired ingame, so there's something I'm missing obviously