Add Universal Media Player to HomeKit - Mute/Unmute and Play/Pause doesn't work

Configuration
1

Hi all:
I’m a beginner of HA and trying to add Logitech Harmony universal remote to HomeKit. Following the documentation of Universal Media Player I have first wrapped the remote with the configuration below:

  - platform: universal
    name: Living Room Media Center
    attributes:
      state: remote.harmony
      source_list: remote.harmony|activity_list
      source: remote.harmony|current_activity
    commands:
      turn_on:
        action: remote.turn_on
        target:
          entity_id: remote.harmony
      turn_off:
        action: remote.turn_off
        target:
          entity_id: remote.harmony
      volume_up:
        action: remote.send_command
        target:
          entity_id: remote.harmony
        data:
          device: >
            {% if is_state('select.harmony_hub_activities', 'Music') -%}
                Stereo Amplifier
            {%- else -%}
                AV Receiver
            {%- endif %}
          command:
            - VolumeUp
            - VolumeUp
          delay_secs: 0.2
      volume_down:
        action: remote.send_command
        target:
          entity_id: remote.harmony
        data:
          device: >
            {% if is_state('select.harmony_hub_activities', 'Music') -%}
                Stereo Amplifier
            {%- else -%}
                AV Receiver
            {%- endif %}
          command:
            - VolumeDown
            - VolumeDown
          delay_secs: 0.2
      volume_mute:
        action: remote.send_command
        target:
          entity_id: remote.harmony
        data:
          device: >
            {% if is_state('select.harmony_hub_activities', 'Music') -%}
                Stereo Amplifier
            {%- else -%}
                AV Receiver
            {%- endif %}
          command: Mute
      media_play:
        action: remote.send_command
        target:
          entity_id: remote.harmony
        data:
          device: >
            {% if is_state('select.harmony_hub_activities', 'Movie') -%}
                Zidoo Player
            {%- endif %}
          command: Play
      media_pause:
        action: remote.send_command
        target:
          entity_id: remote.harmony
        data:
          device: >
            {% if is_state('select.harmony_hub_activities', 'Movie') -%}
                Zidoo Player
            {%- endif %}
          command: Pause
      media_previous_track:
        action: remote.send_command
        target:
          entity_id: remote.harmony
        data:
          device: >
            {% if is_state('select.harmony_hub_activities', 'Movie') -%}
                Zidoo Player
            {%- endif %}
          command: SkipBack
      media_next_track:
        action: remote.send_command
        target:
          entity_id: remote.harmony
        data:
          device: >
            {% if is_state('select.harmony_hub_activities', 'Movie') -%}
                Zidoo Player
            {%- endif %}
          command: SkipForward
      select_source:
        action: remote.turn_on
        target:
          entity_id: remote.harmony
        data:
          activity: "{{ source }}"
    device_class: receiver
    unique_id: livingroom_mediacenter

I then added the following configuration to expose the media player to Homekit:

homekit:
  - name: "Living Room Harmony"
    auto_start: true
    mode: accessory
    filter:
      include_entities:
        - media_player.living_room_media_center
    entity_config:
      media_player.living_room_media_center:
        name: "Living Room Harmony"
        feature_list:
          - feature: on_off
          - feature: play_pause
          - feature: toggle_mute

However I can’t seem to get toggle_mute and play_pause to work. In HomeKit widget when I click the button, nothing happens, and there is no error in the log.
I understand both mute toggle and play_pause are controlled by the media player, and I have tried several things today without luck. Appreciate if anybody who has similar setup can point me where to look!