Elrond Burrell example

gistfile1.php

// place it in functions.php of your active theme
add_action('wpmm_head', 'wpmm_leadin_tracking_code');

function wpmm_leadin_tracking_code(){
  // replace the tracking code with your tracking code
  ?>
    <!-- Start of Leadin Embed -->
      <script type="text/javascript" src="//js.leadin.com/js/v1/2455758.js" id="LeadinEmbed-2455758" crossorigin="use-credentials" async defer></script>
    <!-- End of Leadin Embed -->
  <?php
}