By default, WordPress does not let you add code directly in your posts (or popups). In this article, we will show you how to easily add JavaScript in WP Popups. For that, you will need to copy/paste some code into your theme’s functions.php file to create a custom shortcode and we will use that shortcode inside our popup.
Basically paste this snippet and replace <!– paste your html and javascript here –> with the code you want to insert ( html + js only ! ).
Then in your popup, you can use [wpp_insert] shortcode to print the code.