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