MailChimp submit button doesn't work and the post content changes its position

Slide In plugin doesn't work properly. I setup everything in "Global Settings", but when I try to submit an email for subscription - the requests doesn't go through and once I start typing something in the box, the post content changes it's position by 8px on the right.

Please check the Slide In plugin on my website:

Just scroll until it shows up.

Please let me know what is an issue with this plugin.