First go into apps on your Chromcast Device and look up "Tailscale"

Install Tailscale

Open the Tailscale app

Click on Get Started

The app will notifiy you that it wants to set up a VPN. Press "OK" to set this up.

Take a picture of the QR Code and send to the Admin to be added to the Tailscale network with the Jellyfin Server. Once the admin scans the code, your device will be logged in automatically. 

Make sure that this app is enabled prior to starting Jellyfin. Sometimes when your device reboots, it will not enable the VPN on its own.