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
Dict,
    FrozenSet,
    Iterable,
    List,
    Optional,
    Set,
    Tuple,
    Type,
    Union,
    cast,
    overload,
)
import jinja2
import pendulum
from dateutil.relativedelta import relativedelta
from jinja2.nativetypes import NativeEnvironment
from sqlalchemy import Boolean, Column, ForeignKey, Index, Integer, String, Text, func, or_
from sqlalchemy.orm import backref, joinedload, relationship
from sqlalchemy.orm.session import Session
from sqlalchemy.sql import expression
import airflow.templates
from airflow import settings, utils
from airflow.compat.functools import cached_property
from airflow.configuration import conf
from airflow.exceptions import AirflowException, DuplicateTaskIdFound, TaskNotFound
from airflow.models.base import ID_LEN, Base
from airflow.models.baseoperator import BaseOperator
from airflow.models.dagbag import DagBag
from airflow.models.dagcode import DagCode
from airflow.models.dagpickle import DagPickle