This is what you will get:
The incoming webhook URL as given by flock.com. You can use the same on all your Netdata servers (or you can have multiple if you like - your decision).
Get them here: https://admin.flock.com/webhooks
Set them in
/etc/netdata/health_alarm_notify.conf (to edit it on your system run
/etc/netdata/edit-config health_alarm_notify.conf), like this: