Webhook filter for adding/deleting attachments

I would like to receive event notifications on a project resource when attachments are added/deleted to tasks. Is there a way to create a webhook filter to receive event notifications for this?

So far I’ve tried the following filters with no luck:

    {'resource_type': 'task',
     'resource_subtype': 'default_task',
     'action': 'changed',
     'fields': ['attachments']
     }

and:

    {'resource_type': 'attachment', 'action': 'added'},
    {'resource_type': 'attachment', 'action': 'removed'},
    {'resource_type': 'attachment', 'action': 'deleted'},
    {'resource_type': 'attachment', 'action': 'undeleted'},
    {'resource_type': 'attachment', 'action': 'changed'}

Thanks!

anyone have any thoughts?

Is this possible? The API documentation is very sparse.