Slide-in Plugin doesn't slide in

Recently installed the Slide-in plugin to use as a subscription form for Mail Chimp. Whatever I did in the setup, that thing doesn't appear. It's activated, I checked again, but couldn't make it work. I also tried it on another site to see if it would work elsewhere, but it didn't there either. Don't have a clue why. Couldn't find an answer in the forums either. Any ideas?