The SlackAPIFileOperator is not straight forward and it might be better to add an example DAG to demonstrate the usage.

airflow/providers/slack/operators/slack.py
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import json
from typing import Any, Dict, List, Optional
from airflow.models import BaseOperator
from airflow.providers.slack.hooks.slack import SlackHook
class SlackAPIOperator(BaseOperator):
    """
    Base Slack Operator
    The SlackAPIPostOperator is derived from this operator.
    In the future additional Slack API Operators will be derived from this class as well.
    Only one of `slack_conn_id` and `token` is required.
    :param slack_conn_id: :ref:`Slack connection id <howto/connection:slack>`
        which its password is Slack API token. Optional
    :type slack_conn_id: str
    :param token: Slack API token (https://api.slack.com/web). Optional
    :type token: str
    :param method: The Slack API Method to Call (https://api.slack.com/methods). Optional
    :type method: str
    :param api_params: API Method call parameters (https://api.slack.com/methods). Optional
    :type api_params: dict
    :param client_args: Slack Hook parameters. Optional. Check airflow.providers.slack.hooks.SlackHook
    :type client_args: dict
    """
    def __init__(