Let’s loop in Support, they have a handful of similar tickets, none informative, all show a temporary glitch and the users were able to add them. But, good to get in queue with Support in case this does not resolve itself. If you have other active domains, you can file the ticket under one of those and let the engineer know the domains you’ve tried and are having issues with. If you receive an automatic reply, please reply back and indicate you’re still having the issue.
To contact Cloudflare Customer Support, login & go to https://dash.cloudflare.com/?account=support and select get more help. If you’re unable to create the ticket simply email support AT cloudflare DOT com. Please share your ticket number here as I’d like to keep an eye on it.