I've done GET _nodes too and it doesn't look like any Slack Watcher notifications are enabled - not sure if this is something that I need to enable in addition to adding my webhook. It was too many characters to post here annoyingly.
I'm seeing exactly the same thing (ES 5.6.7 and Kibana 5.6.5):
{
"error": {
"root_cause": [
{
"type": "illegal_argument_exception",
"reason": "no account found for name: [null]"
}
],
"type": "illegal_argument_exception",
"reason": "no account found for name: [null]"
},
"status": 400
}
But the following delivers a message to Slack so it seems the basic account has been set up correctly:
> curl -X POST -H 'Content-type: application/json' --data '{"text":"Yipee this one works…"}' https://hooks.slack.com/services/(url)
that should fix your issue. Note that from 6.2 onwards we are more strict regarding the configuration of those settings, so you will get warnings early on.
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