Mark down card inside custom button card

I’m trying to display the value of an (attr) sensor inside a popup using browser_mod.popup.
Inside that popup i want to use a markdowncard to display the sensor value.
However i can’t get it to work.

type: custom:button-card
entity: input_boolean.sensor_huisvuil
show_entity_picture: true
entity_picture: /local/mijn-container-400px.png
name: Restafval
layout_options:
  grid_columns: 2
  grid_rows: 2
styles:
  card:
    - height: 100%
card_mod:
  style: |
    :host {height: 100% !important}
state:
  - value: "on"
    show_icon: false
    styles:
      card:
        - animation: blink 2s ease infinite
tap_action:
  action: call-service
  service: input_boolean.turn_off
  data:
    entity_id: input_boolean.sensor_huisvuil
hold_action:
  action: fire-dom-event
  browser_mod:
    service: browser_mod.popup
    data:
      title: Volgende ophaling huisvuil
      timeout: 3000
      size: normal
      styles: |
        --popup-min-width: 400px;
        --popup-max-width: 600px;
        --popup-border-radius: 28px;
      card:
        type: markdown
        content: |
          {% state_attr('sensor.limburg_net_afval_restafval', 'Sort_date') %}

Hmm…nobody ?