Filter Wordpress popup content

functions.php

<?php
/**
 * IF you want to filter popups content to add custom content
 * http://wordpress.org/plugins/popups/
 **/
add_filter('spu/popup/content', 'add_gf_to_spu', 10, 2);
function add_gf_to_spu( $content, $popup){
   // Check if the popup is the correct one
   if( $popup->ID == ID_NUMBER_HERE ){
       if ( is_page(THE_PAGE_YOU_WANT) ) {
           $content .= '[my-shortcode-here]';
       }
   }
   return $content;
}