Clients can only connect to a single server at a time. If you list multiple servers they will be treated as a failover list and it will only attempt to connect to the second server if the connection fails to the first server.
If you are having issues connecting the client to the server please double check your server hostname in the client. It should be an IP address or fully qualified domain name and not include any protocol (e.g. HTTP://) or slashes. In addition, check the firewall and port settings on your server to make sure the client can connect to the ports listed in the documentation.
https://www.ni.com/docs/en-US/bundle/systemlink/page/setting-up-systemlink-server.html
In addition, here is a link to a training video that walks through how to correctly install and configure the SL server.
https://learn.ni.com/learn/course/systemlink-2021-installation-and-setup/systemlink-2021-installatio...
