You need to add a DNS record so that Hydrogen can be accessed.
By default Hydrogen will use https://hydrogen.example.com so you will need to create an CNAME record for `hydrogen`. See [Configuring DNS](configuring-dns.md).
If you would like to use a different domain, add the following configuration to your `inventory/host_vars/matrix.example.com/vars.yml` file (changing it to use your preferred domain):