Send temperature via http request

Configuration
1

Hi everyone,

I have several Shelly TRV at home.
Those TRV’s measured environment temperature can be overwritten (as it is infuenced by the radiator) via a simple http request.
You simply visit http://192.168.1.156/ext_t?temp=measured_temperature and write a number in place of “measured_temperature”.
I have tried to write an automation that sends this http request automatically every time the temperature of the sensor sensor.livingroom_average_temperature changes.
I have tried to achieve this by doing the following:

configuration.yaml

rest_command:
  send_temperature_request:
    url: http://192.168.1.156/ext_t?temp={{ temp }}

automations.yaml

automation:
  - alias: Send Temperature via HTTP Request
    trigger:
      - platform: state
        entity_id: sensor.livingroom_average_temperature
    action:
      - service: rest_command.send_temperature_request
        data_template:
          temp: "{{ states('sensor.livingroom_average_temperature') }}"

However it seems not to work as the service rest_command.send_temperature_request seems to not exist. I have obviously tried to reload the yaml configuration but the problem persists.

Could anyone give me some direction?

Many thanks!