I have a mapped domain, a few actually, set up on a multisite installation.
I've set the IP to point to the proper place and everything resolves as it should *except* if I try to map https://www.domain.com, it rolls back to http://www.domain.com.
I can set www. with http just fine, just not with https.
I'm on SiteGround using Let's Encrypt with add-on domains.