Newbie needs help… MQTT action by not working with two cards within a custom card

Hi all,

I’ve only just started using HA after 10 years of being a Domoticz user. I’m still strugling a bit with YAML-configurations so I’m hoping someone can put me on the right track.

I have a ventilation unit that I can control through MQTT and I want to be able to have two cards on my dashboard to control the two most used modes, Auto and High. The weird thing is that if I create a single custom card with this config it works:

type: custom:button-card
show_name: true
show_icon: true
card_size: 2
name: High
tap_action:
  action: call-service
  service: mqtt.publish
  service_data:
    topic: ESP_Duco/cmd
    payload: VENTMODE,PERMANENTHIGH
    qos: 1
    retain: 0
icon: mdi:air-conditioner
show_state: false
styles:
  card:
    - height: 100px

When I try to get both Auto and High on one card with this config I get an error that the action to publish mqtt cannot be done - 'must contain at least one of topic, topic_template.

type: horizontal-stack
cards:
  - type: custom:button-card
    name: Auto
    tap_action:
      action: call-service
      service: mqtt.publish
      service_data: null
      topic: ESP_Duco/cmd
      payload: VENTMODE,AUTO
      qos: 1
      retain: 0
  - type: custom:button-card
    name: High
    tap_action:
      action: call-service
      service: mqtt.publish
      service_data: null
      topic: ESP_Duco/cmd
      payload: VENTMODE,PERMANENTHIGH
      qos: 1
      retain: 0

I’ve spent quite some time trying to see what the problem is but I’m kind of out of options… Is there anyone who can help me figuring this out? Thanks in advance!