custom domain seems to error out - but available with godaddy search -

Hello drewsteele and welcome,

Could you please share your domain name suffix for further review. Also if you are adding your domain into your Business Class Portal make sure you are following Use your existing domain name with Comcast Business email and web hosting.  It is very important that you check your Manage Services.Websites. View Domain Info to make sure that your Comcast MX, CName, PTR records are accurately administered.

Hope this helps you out.