Add log message from the GrayLog to Slack

[gaurang12041999]

I have set up the plugin in Graylog and created Alert using that. And I am successfully able to get the Alert message.
But I want to post the actual log into the slack.

Suppose if my log is "Internal server error. The object doesn't contain xyz field". Then I want to add that log into the slack post as well. It can be any log. And also want to add a partial message in the slack post.

I have taken the reference from the below page. But it didn't work for me. If anyone can help with this. Thanks for your help!!
https://docs.graylog.org/en/4.0/pages/alerts.html#:~:text=The%20Slack%20alert%20notification%20allows,previously%20available%20from%20Graylog%20Labs.