The first thing to do is to upgrade your Netdata. We’re at v1.31 now.
After that, you can sign in to Netdata cloud and then visit your agent’s UI. That records the URL you use.
The next time you get an alarm from that agent, you should be redirected correctly.
Our registry stopped recording URL a while back, because there was no explicit opt-in for it to do so. Signing up to the cloud provides that opt-in and the local registry alternative provides the feature without sending any URLs to Netdata.
I have a similar problem. I have alarms turned on and notifications get delivered to my matrix homeserver.
This is an example notification I received:
myserver needs attention - disk space usage
disk_space._var_lib_netdata (/var/lib/netdata) disk space usage = 15.7% disk /var/lib/netdata space utilization