I am using freedns to manage my domain, and I am trying to add CNAME entries for my custom domain. The CNAME entries appear when I test the domains on dnschecker.com, but the homeassistant cloud webpage is still unable to validate. Any tips?
I am not really sure what you are talking about.
Have you made a CNAME in your own domain pointing to Nabucasa?
If that is the case, then your device will use that CNAME to connect to NavuCasa, but the NabuCasa server does not have your CNAME in its certificate, so SSL will fail.