Mqtt on json message copy entire json to text sensor

ESPHome
1

Hello guys, i know this is a newbie question but i really can’t understand how to do this. this is the relevant extract of my config:

# Example configuration entry
text_sensor:
  - platform: template
    id: last_mqtt_message
    name: Last mqtt message
mqtt:
  broker: broker.host
  port: 8883
  username: user
  password: !secret mqtt_password

  discover_ip: false
 
  discovery: false
  
  log_topic: null

  topic_prefix: null
  birth_message:
    topic: ${mqtt_base_topic}/birth
    payload: online
  will_message:
    topic: ${mqtt_base_topic}/will
    payload: offline
  on_json_message:
    topic: ${mqtt_base_topic}/commands
    then:
      # - lambda: !lambda |-
      #     serializeJson(x, id("last_mqtt_message")); #don't work
      - lambda: !lambda id(last_mqtt_message).publish_state(x); # don't work

how can i simply print all the json string to a text sensor?
Thanks!