Action (Fire event) Service Data not saved (no error)


I created an automation to check my vacuum cleaner has cleaned (i can manually turn it off by the input_bool and i want a reminder to put it back on if needed)

I’m lisening for the event in Node-RED but i would like to pass the ‘LastCleaning’ date in the event_data.
The problem is that the payload will not save after pressing the ‘Save’ button. I don’t get an error while saving. When looking in the Automations.yaml i see an empty line in the event_data section. (as seen below)
Does anyone know what i’m doing wrong?

Payload i would like to send in my event

LastCleaning: '{{as_timestamp(states('sensor.xiaomi_vacuum_cleaner_last_clean_end'), 0)  | timestamp_custom("%d-%m-%Y")}}'

complete automation

- id: '1637067134928'
  alias: Zoef heeft gisteren niet gezogen
  description: ''
  - platform: time
    at: 04:00
  - condition: state
    entity_id: input_boolean.holiday_mode_enabled
    state: 'false'
  - condition: template
    value_template: '{{((as_timestamp(now(), 0) - as_timestamp(states(''sensor.xiaomi_vacuum_cleaner_last_clean_end''),
      0)) /60 /60) > 24}}'
  - event: Zoef_Niet_Gezogen
  mode: single

Template editor seems to accept the syntax.

as you can see, the automation is saved with an empty ‘event_data’