Unfortuantely I don’t know what to do to fix it for you
but I did find some relevant articles that perhaps have the answer for you?
Does the notify_push test work for you in CLI?
ncc notify_push:self-test
If you restart the notify_push service and/or start it manually does it start up then?
systemctl restart notify_push
systemctl start notify_push.service
service notify_push restart
NC Forum topic - Notify Push Service does not start automatically
Also, what does the journalctl -xe say?