Yah, you need to delete the first line
volume:
and remove 2 leading spaces from Every line.
alias: Increase volume
mode: parallel
descrption: >
increase the volume of any media player.
fields:
player:
description: The media player(s)
required: True
selector:
entity:
mulitple: True
domain: media_player
direction:
description: Volume Up or Volume Down
required: True
selector:
select:
options:
- label: Volume Up
value: up
- label: Volume Down
value: down
level:
description: Increment
default: 0.1
selector:
number:
min: 0.0
max: 0.0
step: 0.01
variables:
media_player: "{{ player if player is list else [player] }}"
current: "{{ media_player | map('state_attr', 'volume_level') | select('is_number') | list | average }}"
step: "{{ level | default(0.1) }}"
volume_level: "{{ current + step if direction == 'up' else current - step }}"
sequence:
- action: media_player.volume_set
target:
entity_id: "{{ media_player }}"
data:
volume_level: "{{ volume_level }}"