Create a host, monitored via DNS instead of IP address.
Create the Slack media type + integration, and according actions etc.

Trigger a problem and see the notification fail:
Slack notification failed : Field "host_ip" cannot be empty

Change the mediatype parameter "host_ip" to value "{HOST.DNS}" and it works, but not it doesn't work if a host is monitored via IP address.

Suggested solution: Change the mediatype parameter "host_ip" to value "{HOST.CONN}" so that it will always get atleast one value.