Well, in today's world it's normal for URLs to not have the http or https used so that browsers are not bound to one access protocol or another. Since XenForo is a modern piece of software I assumed that using the URL without the specific access protocol indication would be acceptable (and perhaps even appropriate.)
It just seems a strange design decision for the "Board URL" entry to require that the access protocol be explicitly defined.
It just seems a strange design decision for the "Board URL" entry to require that the access protocol be explicitly defined.