Rounding of sensor values

Configuration
7

I’m fairly new to HA so this might be a stupid question but I don’t manage to get the example of @BertrumUK working.

I tried multiple variation in the configuration and customisation file.

This is the code I’m trying to use, anyone any idea what’s wrong?

# MQTT sensors

  - platform: mqtt
    state_topic: "/sensor1/HUM"
    name: "humidity_slaapkamer"
    unit_of_measurement: "%"
    value_template: '{{ value_json.humidity_slaapkamer.value | round(1) }}'
  - platform: mqtt
    state_topic: "/sensor1/PRES"
    name: "Pressure slaapkamer"
  - platform: mqtt
    state_topic: "/sensor1/TEMP"
    name: "temperature_slaapkamer"
    value_template: '{{ value_json.temperature_slaapkamer.value | round(1) }}'