Ah, that looks like you’re trying to access a restricted area while not logged in. If the site wasn’t available it wouldn’t be able to show that error page.
Just to note, as a hosted customer you can contact team@discourse.org or message @team any time for any support issues (not to disparage our wonderful community support who are also very helpful and knowledgeable 
)
When I go to your original site address as an anonymous user I land on the homepage of your new domain with no issues (though I can’t check the password issue, of course).