I couldn't find any official documentation specifying what each parameter to a `sla_miss_callback` callable are. This would be a great addition to know how to properly format the messages sent.
airflow/models/dag.py
self.default_args['start_date'] = timezone.convert_to_utc(self.default_args['start_date'])
        if 'end_date' in self.default_args:
            self.default_args['end_date'] = timezone.convert_to_utc(self.default_args['end_date'])
        
        if timetable is None:
            self.timetable = create_timetable(schedule_interval, self.timezone)
            if schedule_interval is ScheduleIntervalArgNotSet:
                schedule_interval = DEFAULT_SCHEDULE_INTERVAL
            self.schedule_interval: ScheduleInterval = schedule_interval
        elif schedule_interval is ScheduleIntervalArgNotSet:
            self.timetable = timetable
            self.schedule_interval = self.timetable.summary
        else:
            raise TypeError("cannot specify both 'schedule_interval' and 'timetable'")
        if isinstance(template_searchpath, str):
            template_searchpath = [template_searchpath]
        self.template_searchpath = template_searchpath
        self.template_undefined = template_undefined
        self.parent_dag: Optional[DAG] = None  
        self.last_loaded = timezone.utcnow()
        self.safe_dag_id = dag_id.replace('.', '__dot__')
        self.max_active_runs = max_active_runs
        self.dagrun_timeout = dagrun_timeout
        self.sla_miss_callback = sla_miss_callback
        if default_view in DEFAULT_VIEW_PRESETS:
            self._default_view: str = default_view
        else:
            raise AirflowException(
                f'Invalid values of dag.default_view: only support '
                f'{DEFAULT_VIEW_PRESETS}, but get {default_view}'