Solved!!
- platform: rest
name: Sensore Thingspeak
json_attributes:
- field1
- field2
- field3
- field4
resource: https://api.thingspeak.com/channels/xxxxxx/feeds/last.json?api_key=myapikey
value_template: '{{ value_json.created_at }}'
- platform: template
sensors:
temperatura:
friendly_name: 'Temperatura balcone cucina'
value_template: '{{ state_attr("sensor.sensore_thingspeak", "field1") | round(1)}}'
device_class: temperature
unit_of_measurement: '°C'
other sensor.....
Thanks to the guide and tips here on the forum I created the sensor. A single http request feeds a sensor (last reading time) with 4 arguments (temp, humidity, etc.). With a templete I take the data from the arguments and create individual sensors.