[digiltd]

Hi, just managed to test it out.
Everything works now, a bit different than I imagined, but it is perfect like this. What I mean. If I tell "Alexa, tell Kodi to play Supernatural" I receive the same error again. If I tell to play next episode of Supernatural it is working. Or The Flash, etc.
As for Gantz I had to add G. A. N. T. Z. to the slot. She understands on Guns so it won't work.

 When you say "Alexa, tell Kodi to play Supernatural" that might be because she hears "super natural" (check your logs or the app to see what she is sending).

Also you are using the generic "play" command, which is always going to make things trickier for her. She doesn't know if "supernatural" it is a show, a movie, a video playlist, an audio playlist, a band, an album, a song etc. But when you say "play the next episode of the supernatural" she then knows it is a tv show because she heard to word "episode".

You might find saying "play the tv show supernatural" works better.