Extra_data_template in custom-ui

Configuration
1

@andrey

I’m trying to get the date and time of a calendar event into the extra_data_template area of my sensor.

This works and displays correctly (kind of…) as a standard sensor:

- platform: template
  sensors:
    next_event_template:
      friendly_name: "Next Event"
      value_template: "{{ (states.calendar.<mycalendar>gmailcom.attributes.message) }} on {{  as_timestamp(states.calendar.<mycalendar>gmailcom.attributes.start_time) | timestamp_custom('%-m-%-d-%Y @ %H:%M') }}"

Then If I remove the timestamp section from the sensor and add it to the customize section like this:

sensor.next_event_template:
  icon: mdi:calendar-alert
  extra_data_template: ${as_timestamp(states.calendar.,mycalendar>gmailcom.attributes.start_time) | timestamp_custom('%-m-%-d-%Y @ %H:%M')}

I get:

ex

But the extra_data_template doesn’t show up below.

Is the code that I’m trying to use supported or is there a different way required?