From the community.istaria website:

We're making some changes to the domain records.

Horizons Players!

We're making some changes to the domain
records. There's a possibility that there will be a disruption in the
accessing the web sites over the next few days. In the interest of
making sure you can still connect, please write down the following url
and place in a box with a glass lid. Break glass in case of Emergency.
https://68.142.64.212/Default.aspx

Or you could just type it into your browser.

Thank you,

Horizons Customer Support