Acess with diffent hostnames

Hello,

i´ve installed an ready-to-go minimal debian image with jitsi on my root server.
The server has 2 hostnames:

xxxxx.happysrv.de (Standard from my data center)
yyyyy.ddnss.ch (i set this one up manually)

When i access JITSI through the xxxxx.happysrv.de adress, everything works fine, audio and video.
When i type yyyyy.ddnss.ch in the Browser i still get my JITSI Start page and i can start a session, but i don´t get audio or video.
The browser ask me if i can access this ressources on my macbook and i say yes,but it doesn´t work.
I can´t also stop the session with the red button.
I don´t know where to start to debug this or what could be wrong.