NOOB: Controlling Panasonic TV

Hi,

New to HA - installed via Hass.io on RPi. Using Unifi Controller integration.

My Panasonic TV shows up in the Entity Registry as media_player.65fz950_series and panasonic_viera.

When I toggle the on/off switch on the Overview page for this device I get an error:

2019-08-14 18:02:47 ERROR (MainThread) [homeassistant.components.websocket_api.http.connection.547912126096] HTTP Error 500: Internal Server Error
Traceback (most recent call last):
  File "/usr/src/homeassistant/homeassistant/components/websocket_api/commands.py", line 128, in handle_call_service
    connection.context(msg),

I’m new to HA so I’m not sure whether it’s an actual error or I need additional integrations/add-ons or configuration to make this work???

NEW: I’ve noticed that my TV turns on when I restart HA. But I still get the 500 error when trying to toggle it off on the Overview page.