Webostv help

Noob here need some help please, i have gotten a script that will send mute command to my tv but it wont un mute it.

  - data_template:
      is_volume_muted: "{{ not state_attr('media_player.living_room_tv', 'is_volume_muted') }}"
    entity_id: media_player.living_room_tv
    service: media_player.volume_mute