Unable to display a video with a custom player

Port 80 is used by the Apache which runs the Kaltura API and web interfaces. Port 88 is used by Nginx to serve HLS, HDS and DASH manifests for playback.
Both need to be accessible from all clients you intend to use. Like I wrote above, you can change the Nginx config to use a different port and adjust the kaltura.delivery_profile records accordingly.