Chances are the URL for the domain may be entered incorrectly in the settings of the Splash page.

To check, head to the Settings tab of your event page's toolbar.

If you have http:// or www. (or both) in the Vanity URL, go ahead and remove it. It's not necessary! Click save, and you'll be all set.

If you're still having issues, check to make sure your DNS settings are set up correctly within the custom domain. Feel free to submit a request at the top of the page if you're still having trouble!