Hi. If you want to use the internal XMPP server you don’t have to setup a server or BOSH etc. Also turn/stun configuration isn’t needed. (internal XMPP server doesn’t support WebRTC yet)
You don’t have to follow https://github.com/jsxc/jsxc/wiki/Install-ojsxc-(owncloud) it’s just as simple to enable the app and choose to use the internal server.
I would try to reinstall the app.