AppDaemon Sequence not working

I’m struggling to define a sequence in apps.yaml and asking for some advise.

After the definition of the apps, I have created a simplest possible sequence:

sequence:
  proximity_off:
    name: Prox OFF
    steps:
    - sleep: 3

But appdaemon is not accepting it:

2025-06-22 11:05:10.440191 WARNING AppDaemon: ------------------------------------------------------------
2025-06-22 11:05:10.440763 WARNING AppDaemon: Unexpected error during utility()
2025-06-22 11:05:10.441344 WARNING AppDaemon: ------------------------------------------------------------
2025-06-22 11:05:10.444283 WARNING AppDaemon: Traceback (most recent call last):
  File "/usr/lib/python3.12/site-packages/appdaemon/utility_loop.py", line 173, in loop
    await self.AD.app_management.check_app_updates()
  File "/usr/lib/python3.12/site-packages/appdaemon/app_management.py", line 796, in check_app_updates
    await self.check_app_config_files(update_actions)
  File "/usr/lib/python3.12/site-packages/appdaemon/app_management.py", line 621, in check_app_config_files
    self._compare_sequences(update_actions, cfg, files_to_read)
  File "/usr/lib/python3.12/site-packages/appdaemon/app_management.py", line 1093, in _compare_sequences
    existing_sequences = set(self.sequence_config.root.keys())
                             ^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'root'
2025-06-22 11:05:10.444897 WARNING AppDaemon: ------------------------------------------------------------

Any hint welcome - thanks!