If a fully qualified domain name is used, this must be an exact match. Standard SSL certificates are created to function with one unique fully qualified domain name. This is the base domain name plus any prefix (sub domain).
By popular request, you can also add an ip address (for example: 127.0.0.1, 192.168.1.2, etc) or any internal domain name (for example: localhost, mobilefish.intranet, research.mobilefish.local).
The setting is required.
For example: If you intend to secure the url https://www.mobilefish.com, then the common name must be www.mobilefish.com.
