The CLI set command is primarily an undocumented function used for testing, it doesn’t report errors. There is no app.server_search_domain option. The search domain option is in the server settings that is unique to each server.
The server settings are available by clicking on the name of the server.
The DOMAIN-SEARCH option has been added to codebase and will be used when multiple DNS search domains are included. This change will be included in the next release.