How to setup alert notification on flock

Hi all,
i’m setting up my first alert on grafana v9.0.0 with this new update there are lot of new features and i want use Custom Alertmanager Templates mean i want send custom massge on flock channel can some give me walk through how cloud i setup my alert on flock.
below is my message template pls check if have done mistake

And also im able to test my alert getting this error

can someone guide
thanx.