Can somebody guide me on how to install it on the Drupal 9, the website says to download the module and what next where I’m going to out the API token, what would be the pull URL.
You shouldn’t need to set the API token, you just need to define the CDN url that will be rewritten for all static assets.
The end goal is to ensure URLs rendered like
yourdomain.com/sites/all/themes/yourtheme/style.css get re-written to
<yourCDNprefix>.cdn.shift8web.com/sites/all/themes/yourtheme/style.css. Do you follow so far?
If your still confused, you could paste a screenshot of the settings page that you are having trouble with.
Let me know if I can help further!