I try to avoid using the GUI to configure/run barrier so I created a simple bash script barrier-client.sh to launch my barrier client. It reads from a .config/barrier.cfg file I created to determine the client name and server to connect to.
cat ~/.config/barrier.cfg
BARRIER_CLIENT_NAME=${HOSTNAME}
BARRIER_SERVER=gilbert.lan:24800
This expects the client to already be configured to trust the server. That trust is managed by the ~/.local/share/barrier/SSL/Fingerprints/TrustedServers.txt which should have the fingerprint of the server.