Error parsing value: 'value_json' is undefined

Hi,

I have this configuration for an MQTT switch.
The hardware is a NodeMCU (ESP12) with Tasmota firmware

I get this error:

Error parsing value: 'value_json' is undefined (value: , template: {{ value_json.POWER }})

This is my config:

switch:
  - platform: mqtt
    name: damian_radiator_switch
    # state_topic: "/DOMUS/DAMIAN/RADIATOR/RESULT"
    state_topic: "/DOMUS/DAMIAN/RADIATOR/STATE"
    value_template: "{{ value_json.POWER }}"
    command_topic: "/DOMUS/DAMIAN/RADIATOR/cmnd/POWER"
    availability_topic: "/DOMUS/DAMIAN/RADIATOR/LWT"
    qos: 0
    payload_on: "ON"
    payload_off: "OFF"
    payload_available: "Online"
    payload_not_available: "Offline"
    retain: true

I received this message in the state_topic: “/DOMUS/DAMIAN/RADIATOR/STATE”.

{
    "Time": "2021-10-20T11:22:02",
    "Uptime": "0T05:28:09",
    "UptimeSec": 19689,
    "Heap": 27,
    "SleepMode": "Dynamic",
    "Sleep": 50,
    "LoadAvg": 19,
    "MqttCount": 1,
    "POWER": "OFF",
    "Wifi": {
        "AP": 1,
        "SSId": "WSP",
        "BSSId": "FC:EC:DA:E9:58:CA",
        "Channel": 11,
        "RSSI": 50,
        "Signal": -75,
        "LinkCount": 1,
        "Downtime": "0T00:00:03"
    }
}

This is in JSON format and have de POWER key (“ON” or “OFF”). I don’t understand the error.
It seams that it don’t recognize the “value_json”

Thanks in advance!