Check box linked to object state

Hi.

I have a slide in Storyline 360 where I want a user to tick a check box to show they have read a document. I then link this into a custom button for progressing to the next slide - the button is in hidden state until you select the check box. This works fine with a simple trigger.

However, I would like the custom button that moves to the next slide to disappear again if the user un-ticks the check box. I can't get this to work. I've tried True False variables as well as triggers but with no luck.

I'm sure I'm just being daft and it is quite easy, but could anyone give me some advice how to do this?

Thanks very much!

Matt