Hi @OCX,
For the Nginx-RTMP-Kaltura integrations, the best doc to follow is https://blog.kaltura.com/free-and-open-live-video-streaming.
If something does not work, check the HTTP requests going out when you hit play, in particular, the playManifest request the player makes. Then make the same request with curl and look at the response.
Feel free to share your findings here for additional guidance.