double check the payload being sent includes the keys Slack expects

I am trying to upload file from github actions to slack, I got the following error

"no custom payload was passed in, using default payload that triggered the GitHub Action axios post failed, double check the payload being sent includes the keys Slack expects Error: no_text Error: Request failed with status code 400"

The following is what I entered in .yml file

  - name: Send GitHub trigger payload to Slack Workflow Builder
    id: slack
    uses: slackapi/slack-github-action@v1.21.0
    with:
      payload-file-path: "./stats.json"
    env:
      SLACK_WEBHOOK_URL: ${{ secrets.SLACK_WEBHOOK_URL }}

could you let me know what am I missing?