This help page describes thin client licensing as follows.

If you have a multi-server application and want to allow connections to more than just one server, each must be licensed to allow client connections.

This help page describes thin client licensing as follows.

It is common for one of your server keys to allow many thin client connections and the others to have few or none. Licenses are shared between servers after configuration. Always do the work of configuring your Thin Client Server list on the computer that has the licenses. It will be the first server added to the server list. When you add other computers to the list, the licenses will be synchronized to those other servers and saved to them.
Once the setup is complete, the order of the server list may be changed, but the name of the server with the licenses can never be removed from the list. If you do this, all the other servers will also lose the licenses.

Confused how both of these can be true at the same time.

Great point. I'll submit a report on this to see if we can update the top page. Here is the most concise description of the licensing I can find. Note the part on clusters (ie: Applications with server lists).

Licensing for VTScada Thin Client Servers

VTScada Thin Client Servers and the connections made to them are subject to the following licensing restrictions:

• Your VTScada license controls whether the server is enabled.
• The server is enabled in VTScadaLight installations, with one allowed connection.
• The number of concurrent VTScada Internet Connections you can make to a server is subject to your VTScada license.
• Depending on the licensing options you purchased with VTScada, you might have the privilege of connecting from zero to unlimited VIC workstations to your server.
• Licenses are managed based on a cluster of configured servers. For example, if one server in the cluster is licensed for 5 connections and another is licensed for 10, you will always have 15 available connections. If the 10-license server goes offline temporarily, your available license count will not drop to the remaining 5 but will remain at 15 on the server that is still running. No existing connections will be lost.
• VTScadaLight licenses may have one Thin Client connection from the local network. Remote computers must connect to the local network using a VPN.

To be clear, in the cluster scenario above, if one server has five thin clients and another has 0, either server can be the thin client server and the total number of licenses for concurrent connections will be five.

Thanks. I was testing & things didn't work the way I expected. Wasn't sure if my system was misconfigured or if my licensing was the issue until you cleared that up.

The licensing described here is similar to mine.

To be clear, in the cluster scenario above, if one server has five thin clients and another has 0, either server can be the thin client server and the total number of licenses for concurrent connections will be five.

One of my thin client servers has unlimited thin clients and the other has zero. How do I establish a connection to the cluster when the server with the unlimited licences is unavailable?

When I open up the Thin Client/Server Setup from the VAM all the URL's in the bottom of Realms tab point to the server with the unlimited licences. When I use the link instead of the thin client opening I get the error shown below.

So in your application settings, your application has to be setup with both servers in the server list (The easy thing is to use basic mode to ensure that this is the case for all services). Next up, in the VAM (VTScada Application Manager), you'll need to ensure that you have URL's which point to each server (Typically having the server name for local resolution there is good and you can also add the server names for other resolution).

IE:

VAN Internet Client Settings Server List:
ScadaPC1
ScadaPC2
www.sv1.ScadaIsCool.com
www.sv2.ScadaIsCool.com

(Then client connections will get the server list regardless from where the connect and will attempt connections in the order provided. Having the LAN/WAN resolvable addresses will let VTScada know who to sync the lists between the servers. (~(I think)~) )