Ability for forms to NOT submit data to MaiilChimp (checkbox opt in)

Hey hey Webflow!

Quick one for this site: http://collectivecamp.us/signup

We have a checkbox: “Keep me updated via email” etc. stating that if they click it, they will get emails (via MailChimp).


However, how do I add a condition so that if it’s NOT ticked, they will not be added to the list etc.?