Can I install an SSL Certificate on a Parked Domain in cPanel?
So, you want to secure a parked domain in your cPanel with an SSL Certificate and make it accessible via secure connection, e.g. https://example_alias_domain.com.
It is not actually possible to install a separate certificate for a parked domain. The parked domain and the main domain can only have one SSL certificate assigned to both.
Note: it is not possible to secure a parked / alias domain using the NamecheapSSL plugin.