Cannot receive the warn notification

when I test the notifier, I can receive the error notifications, but not warn notifications.
My configuration:
[notifier.kafka]
class-name="http"
interval=60
threshold=2
extras={region='us'}
send-close=false
template-open="/etc/burrow/notifier.tmpl"
url-open="https://oapi.dingtalk.com/robot/send?access_token=xxxxxxxxxxxx"

{
"msgtype":"text",
"text":{
"content":"region:{{index .Extras "region"}}\nid:{{.ID}}\ncluster:{{.Cluster}}\ngroup:{{.Group}}\nstart:{{.Start.Format "Jan 02, 2006 15:04:05 UTC"}}\ntotalLag:{{.Result.TotalLag}}"
}
}

I change the threshold to 1, but it still not work. I cannot find the error log about the notifier, how to fix it?

Start by reproducing the notifier behavior with the supplied notifier.kafka configuration, comparing delivery of error and warn notifications. Trace the notifier entry point and its logging while testing a warn condition. Done means warn notifications are delivered reliably and notifier failures provide an actionable log message.

Written by the indexing model from the issue text.