Logstash output-http plugin error 500 when trying to send to slack webhook

Solution 1:

Apparently logstash has issues with double quotes, I am surprised (and disappointed). Here is working code:

  if "error" in [tags] {
    http {
      http_method => "post"
      url => "https://hooks.slack.com/services/<MY_ID>"
      format => "message"
      message => '{"text":"hello"}'
    }
  }