Statistics sensor on top of an MQTT sensor doesn't show sensor

So I’ve tried to use statistics sensor for the folloiwng MQTT sensor

- platform: mqtt
  state_topic: "benita/mq135/1/in"  
  name: "CO2 Level Livingroom"
  unit_of_measurement: "ppm"
  value_template: '{{ value_json.svalue | round(1) }}'
  force_update: true
- platform: statistics
  entity_id: sensor.co2_level_livingroom
  sampling_size: 1000  

The thing is the statistics sensor doesn’t appear, even after many values have been reported by the MQTT sensor back to HA

Any help is appreciated here
Thanks !