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: https://email.mailings.geekbeacon.org/u/MAGIC_TOKEN_GOES_HERE

The domain I have registered with mailgun is mailings.geekbeacon.org. 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 mailgun.org )

Anyone run into this before?