Does tap action service call support templates?

[totalitarian]

Hoping to implement something like so but get an error saying required key data[oscillating] missing

        tap_action:
          action: call-service
          service: fan.oscillate
          data: >
            {% if state_attr('fan.living_room_fan', 'oscillating') %}
              {'oscillating': false }
            {% else %}
              {'oscillating': true }
            {% endif %}

[piitaya]

It's not supported and will not be supported because action is a complete object.
But you can easily doing this by creating a script ! 😊

[krazos]

Is this a technical limitation, and is it specific to templates within the call-service action? I have a slightly different use case where a script isn't really helpful:

I have an entity card for my TV. If the TV is off, I want the tap_action to turn on the TV, but if the TV is already on, I want the tap_action to navigate to another view with a custom remote control card. I accomplish this currently by using two conditional cards for the TV that are identical but for the tap_action, but this is a bit clunky...

[piitaya]

Yes it's a technical limitation. Template is string and is rendered server side. Tap action is JSON object are created front side. It will be too complex to add this support and I do not prefer to add complexity to Mushroom.
Using conditional card is preferable.