Kayn Ult in to Xin after doing DMG Not letting me ult

I dunno whats going on but the two past games ive played against a xin as Kayn, I do dmg to him and try to ult as Kayn and nothing happens, I dont do dmg, I dont jump in for the Umbral Trespass. I just do nothing. Even though my guide says I can ult and the arrows are blue, it wont let me ult in to him??????