I’m getting a security error when I access my podcast via its custom domain.

Unfortunately, you cannot just add https:// to the URL for a domain and expect it to work. Only websites which have SSL certificates can be served via https://. Fireside itself has a SSL certificate, as does all of its subdomains (like yourpodcast.fireside.fm), so they are served securely via https://. Just adding your custom domain to Fireside doesn’t create a SSL certificate for it.

Fortunately, we have developed a (free!) SSL certificate acquisition and integration feature for customers with custom domains. Just flip the toggle switch in your Domains section to turn it on.