Let's Control It

seemed to be missing the "IDX" field in my setup. I have seen other screenshots with the IDX field. Am I doing something wrong?
Thanks,

The plugin got no values so it will not broadcast anything, thus no need for IDX?

I want to control the player with Domoticz, different sounds for different situations. According https://www.letscontrolit.com/wiki/index.php/MP3_player it should be possible with MQTT. I thought that I should have an IDX for MQTT?

No you don't use IDX for that, use rules and publish (preferably) events which the unit then act upon.

As far as I know, the IDX value is only used on sending sensor values to a controller.