Broken Unsubscribe Link with Mailgun

I have a newsletter configured via mailgun. I’m using the private API key in the configuration but when the user clicks on the unsubscribe link they are redirected to:

The domain I have registered with mailgun is When I checked the settings that mailgun suggested all the DNS settings match.

The unsubscribe link gives me a SSL certificate mismatch because go figure, the hostname doesn’t match the certificate. (aka my own domain has a different SSL certificate from )

Anyone run into this before?