Can't retrieve attributes

[ggonmar]

It may be matter of me not being savvy enough on HA, but I'm trying to get the huddle_state of the entity I'm pulling, to no avail:

From documentation, given the sensor sensor.slack_g, there is an attribute called huddle_state.

I've set up a template sensor as follows:

sensor:
  - platform: template
    sensors:
        slack_huddle:
             value_template: "{{ states_attr('sensor.slack_g', 'huddle_state') }}"

But it's showing a permanent "Unavailable. The same happens with other attributes.