The domain you access points to the Nasqueron PaaS, generally used to serve applications through Docker containers.
There isn't any web server configuration for this domain. As such, it's not possible to serve it.
The most probable causes are a new service currently in deployment, a typo in the domain part of the URL or a DNS record error.
First, check the address you used is written correctly.
Then, if you followed a link through a website, it's probably a bug. You can report it as a server outage, to be investigated.
If you're currently configuring the service, the next step is to provide a nginx configuration in the operations repository, to be put in the roles/paas-docker/nginx/files/vhosts container. The filename must match the Docker service/application name (and not the container name).
Finally, if this is your domain and you never intended to host it on the Nasqueron PaaS, you can check your CNAME, A and AAAA records, it probably points to us.