What is wrong with this template?-

Configuration
1 
  - platform: template
    sensors:
      redback_tilbage:
        friendly_name: Græsset er klippet kl.
        value_template: '{{ as_timestamp(states.timer.redback.attributes.finishes_at) | timestamp_custom ('%H:%M') | replace (" 0", "") }}'

image

work in dev.template

image
image768×324 21 KB

2

Your outside quotes and inside quotes are interfering with each other. Use " outside and ’ inside. "{{ … ' … ' … }}"

3 
  - platform: template
    sensors:
      redback_tilbage:
        friendly_name: Græsset er klippet kl.
        value_template: "{{ as_timestamp(state_attr('timer.redback', 'finishes_at')) | timestamp_custom ('%H:%M') | replace (' 0', '') }}"
4

Perfect ! it works Thanks !