I can't bind widget button to event "input on touch begin"

Hi

I recently got this in-game widget button set up: https://answers.unrealengine.com/questions/1048599/view.html

And then I changed my project settings so that “mouse makes touch events”

I successfully have introduced touch events to other blueprints but CANNOT BIND THE target ‘button play’ to Input Touch Begin — even if I drag from the pin and say “assign to…”

It’s really weird because on my first attempt I was successul, but then I thought I’d not do touch events so I changed it back, but then I decided yes I will do touch events, so I am trying to re-code the blueprint and drag and assign/bind, but it won’t work!

Help??