cannot chat in application, getting error message but no detail on server log

[guntutur]

Here's the error message:

Error : Cannot communicate with the call server. Please insure that your browser is websocket capable, or your network doesn't block them.

do i need to configure something?
i'm connected with my coworker through local area network, and had set up the ip accordingly on webapp.properties.json on web client, but still got no luck

would appreciate any pointer, thanks!