MQTT entity not appearing when state_topic is included

Configuration
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1

Hi,

I’m relatively new to home assistant. I have done a recent install and am currently on the latest version. I was starting to get my head around the process of adding a new MQTT entity. I was having a bunch of trouble, however I managed to make it work with the following code.

light:
  - platform: mqtt
    name: "TEST LED RGB CONTROL"
    command_topic: "matt/test/led"
    payload_on: "ON"
    payload_off: "OFF"`

SO,

It worked, which was great. I then added the follow state_topic

light:
  - platform: mqtt
    name: "TEST LED RGB CONTROL"
    state_topic: "matt/test/set"
    command_topic: "matt/test/led"
    payload_on: "ON"
    payload_off: "OFF"

And suddenly the previous entity cannot be found. The same situation happened if I try to add LED controls.
I also tried it with optimistic: false (I don’t know what it does, the documentation seemed like it was a good idea)

Any help is appreciated!

2

Please post the configuration for the other light(s) as well.

3

Both configurations are in the original post.

The first configuration allows me to see the light, the second is the change I made and it disappeared.

4

If it “disappeared” that means Home Assistant detected a syntax error and refused to load it.

Did you check the system log for errors?
Did you run a Config Check?