Integrating cloudways CDN to my Codeigniter project

I have set up CDN on Cloudways and was given a CDN Url. This I understand I need to add to my web application built on CodeIgniter.
I tried what solutions I could find on the web but it's either I'm not doing it right or it simply does not work.

I created a new helper file (cdn_helper.php) in my controller folder

PHP Code:

function cdn_base_url($uri)
 
{
   $currentInstance =& get_instance();
   $keybasedcdnUrl = $currentInstance->config->item('cdn_based_key_url');
   $extensions = array('css', 'js', 'jpg', 'jpeg', 'png', 'gif','pdf');
   $pathParts = pathinfo($uri);
 
   if (!empty($keybasedcdnUrl) && in_array($pathParts['extension'],$extensions)) {
       return $keybasedcdnUrl . $uri;
   }

   return $currentInstance->config->cdn_base_url($uri);
} 


Then I added this line to my config file

PHP Code:

$config['cdn_based_key_url'] = 'https://457224-1431795-raikfcquaxqncofqfm.stackpathdns.com/'; 


It didn't work. However, I read something about setting my own prefix to extend the URL helper

PHP Code:

$config['subclass_prefix'] = 'MY_'; 


 
when I change the prefix to something like this 'ext.'; it gives an error.
please how do I properly integrate CDN?