replacing multisite subdomain with new toplevel domain

I have set up multisite on wpengine and I want to replace one of the subdomains (http://freedee.the3doodler.com) to a top level domain (3doodler.hu). I asked the hosters of 3doodler.hu to update their a-record to 50.116.16.37. When I go to add the mapped domain I get the "domain name is unavailable to access" error. What am I doing incorrectly? Do I need to ask them to add a CNAME as well and if so, to what?

thanks!

Faraz