Be sure to hit save! Just leave that tab open, or close it and go back to the main tab to make a test call.
To use WSS as a transport, rather than WS, the WebSocket Server URL on the Expert Settings page should use the "wss" prefix and you should have configured Asterisk's HTTP daemon for tls operations - disabled by default, and when enabled defaults to port 8089.
Make a test call
Restart Asterisk, or start Asterisk if you haven't already.