'Object not found' for sleep(start_date, end_date, object_id)

[feur]

I'm getting a:
raise exceptions[code](code, message, getattr(exc, 'response', None))
misfit.exceptions.MisfitBadRequest: (MisfitBadRequest(...), u'Object not found')

I can confirm I'm getting the correct object_id from device().id and that the start_date & end_date inputs are valid as I'm getting a correct return from summary()