The most common reason for the message above is that www is not added to your DNS zone file. Please add www under your DNS Settings by making a CNAME record of www as an alias to your domain.com.
Note: This error message will also be displayed if you are on direct.yourdomain.com, or a similar subdomain.
How to set it up correctly for sub-domains?
What are steps to make this plugin work on subdomains, e.g. blog.simplemediacode.com