This usually happen on new accounts and all webinar URL look like:
This happen because subdomain was not created in Settings -> General.
After SubDomain is configured, all webinar URL will correct generated:
Webinar URL is something that you will share over email, chat, social media etc and should be customized to your name, niche, etc.
We don't allow webinars to point on http://members.webinarx.io for a good reason. Members is for members, not public access.