Also for that app you can configure a TURN server, which is necessary for some NAT systems and need to be installed the same way as shown in the linked topic.
But actually I also did not manage to get it running (spreed video calls, Spreed.ME works fine) so far, have always black screen which might be related to a wrong given TURN url. I sadly do far did not get some answer on how to set this right: [Spreed video calls] Black screen / How to set STUN/TURN