To enable full functionality, the installation process is simple!  Follow the checklist instructions below:

Step 1.) Disable the 'buy it now' button in Customize.

From your Shopify admin portal, go to "Online store" and open "Customize" of the required theme.  From there, open the Product page preview and choose the Product pages section.  Turn off the 'Show dynamic checkout button' checkbox.

Step 2.) Disable Shopify users functions.

Go to ‘Settings’ -> Checkout. In the section of ‘Customer accounts’, select ‘Accounts are disabled’.

Step 3.) Add Scripts

Go to ‘Settings’ -> Checkout. In the section of ‘Additional scripts’, add the follow and Save.

{% if first_time_accessed %}
  <script id='_orderStatusLoadJsId' data-token='{{checkout.attributes.agToken}}'>
      var _url = '';
      var l = document.createElement('link');l.rel  = 'stylesheet';l.type = 'text/css';l.href = _url+'stylesheet/sei.css'; = 'all';var h = document.getElementsByTagName('head')[0];h.appendChild(l);
      var s = document.createElement('script');s.type = 'text/javascript';s.async = true;s.src = _url + 'shopify.js';var x = document.getElementsByTagName('script')[0];x.parentNode.insertBefore(s, x);
{% endif %}

Finally, make sure to save your changes!