First you create your CTA Overlay, then use the dropdown menu in the right hand column to associate that CTA.

What is a CTA overlay?

An overlay page allows you to display a small non-intrusive overlay on the destination website to advertise your product or your services. You can also use this feature to send a message to your users. You can customize the message and the appearance of the overlay right from this page. As soon as you save it, the changes will be applied immediately across all your URLs using this type. Please note that some secured and sensitive websites such as google.com or facebook.com do not work with this feature. You can have unlimited overlay pages and you can choose one for each URL.

• CTA Contact
  Create a contact form where users will be able to contact you via email.
• CTA Poll
  Create a quick poll where users will be able to answer it upon visit.
• CTA Message
  Create a small popup with a message and a link to a page or a product.
• CTA Newsletter
  Create a small popup form to collect emails from users.
• CTA Image
  Create a small popup with an image of your choice.
• Coupon
  Create a small popup with a coupon code that users can use.

Check out our article: Using CTA for Marketing