Use the FQDN including the subdomain for the website. According to the Firepower Management Center Configuration Guide, Version 6.61, when you create a URL object, you must use the fully qualified domain name (FQDN) of the website, including any subdomains, and omit the protocol prefix (HTTP or HTTPS). For example, to match www.example.com, you must enter www.example.com as the URL object value, not http://www.example.com or
https://www.example.com. The system automatically matches both HTTP and HTTPS traffic for the same FQDN. Specifying the protocol to match (HTTP or HTTPS) is not required and will result in an invalid URL object. Using the subject common name from the website certificate or defining the path to the individual webpage that uses HTTPS are not supported options for URL objects.