Since 2018 R3 SaveItemConfiguration should also work in Smart Client (documentation is unfortunately outdated), but the serverId must be for either a Management or Recording Server known by the Smart Client.
The error you are getting indicates that this is not the case with the one you are using.
but in our try/catch we got: VideoOS.Platform.ArgumentMIPException: Server with serverId not found
the return from anotherServerID.ServerHostname is the ip(in the SC login we added ip:port for the server, along with basic auth and our user/pass that we created) for our Enterprise(non plus) 2019 R1 recording server.
How can I get the server when we’re in our SC plugin?
VideoOS.Platform.ArgumentMIPException: Server with serverId not found
at VideoOS.Platform.ConfigurationItems.IConfigurationChildItem..ctor(ServerId serverId, String path)
at VideoOS.Platform.Configuration.SaveItemConfiguration(ServerId serverId, Guid pluginDefinitionId, Item item)
at OurArchive.Admin.OurItemManager.SaveJobConfiguration(Item currentItem, Job job) in [D:\sources\Aug15](file:D:/sources/Aug15) 0855 sep13\OurArchive\Admin\OurItemManager.cs:line 344
Sorry. I was not aware that you were running on eCode (non-plus) products. For these products it is unfortunately correct that the SaveItemConfiguration method is not supported in the Smart Client.