title: Unable to upload html file from Jenkins to Slack channel
body: <p>I am sending build start, success and failure notification to slack channel which is working fine only upload file is not working. I am using same token for sending notifications to slack channel which works fine. Not sure how to pass the token in upload file slack api. </p>
  
  <p>I have used below in my pipeline script.</p>
  
  <pre><code>        sh 'curl --request POST \
          --url https://slack.com/api/files.upload \
          --form token=$SLACK_CREDENTIAL_ID \
          --form channels=channel_name \
          --form file=@newman/Sanity.html'
  </code></pre>
  
  <p>Getting error: {"ok":false,"error":"not_authed"}</p>
  
  <p>How to pass token here? as its not reading the token</p>