ErrorDocument 404 404 php is not working in htaccess file in PHP

Question

This is the Content of my .htaccess file is:

ErrorDocument 404 /404.php 

It is in the root directory and the 404.php file is also there. The problem is that when I misspelled the URL, 404.php it doesn't open. Instead, I am getting this message:

Not Found

The requested URL /mywebsite/ites.php was not found on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

But when I tried ErrorDocument 404 google.com, it worked. Can Someone please help me with this?