send notification from Prometheus alertmanager to Google Chat room - kubernetes

Question

we recently started using Google Chat in our organisation therefor we need to send alerts from Prometheus-Alertmanager to Google Chat room. below is my alertmanager config for Google chat
receiver:
- name: 'gchat-receiver'
webhook_configs:
- url: "https://chat.googleapis.com/v1/spaces/AAAArcv5Snw/messages?key=KEY&token=TOKEN"
send_resolved: false
and when we implementing above config we are getting below error in our alertmanager logs:
level=error ts=2021-02-23T06:23:43.931Z caller=dispatch.go:309 component=dispatcher msg="Notify for alerts failed" num_alerts=2 err="gchat-receiver/webhook[0]: notify retry canceled due to unrecoverable error after 1 attempts: unexpected status code 400: https://chat.googleapis.com/v1/spaces/AAAArcv5Snw/messages?key=KEY&token=TOKEN"
level=error ts=2021-02-23T06:23:43.971Z caller=dispatch.go:309 component=dispatcher msg="Notify for alerts failed" num_alerts=1 err="gchat-receiver/webhook[0]: notify retry canceled due to unrecoverable error after 1 attempts: unexpected status code 400: https://chat.googleapis.com/v1/spaces/AAAArcv5Snw/messages?key=KEY&token=TOKEN"
level=error ts=2021-02-23T06:23:43.976Z caller=dispatch.go:309 component=dispatcher msg="Notify for alerts failed" num_alerts=21 err="gchat-receiver/webhook[0]: notify retry canceled due to unrecoverable error after 1 attempts: unexpected status code 400: https://chat.googleapis.com/v1/spaces/AAAArcv5Snw/messages?key=KEY&token=TOKEN"
level=error ts=2021-02-23T06:23:43.994Z caller=dispatch.go:309 component=dispatcher msg="Notify for alerts failed" num_alerts=2 err="gchat-receiver/webhook[0]: notify retry canceled due to unrecoverable error after 1 attempts: unexpected status code 400: https://chat.googleapis.com/v1/spaces/AAAArcv5Snw/messages?key=KEY&token=TOKEN"
any help or guidance on this would be highly appreciated

Answer 1

That is because Google Chat expects a specific JSON payload schema to be posted to that webhook address and the default Alertmanager payload doesn't match it, so you get HTTP 400 response: bad request.
You might need to put a custom application in between to transform the JSON to Google Chat acceptable format. There are already some repos in Github that match that general criteria as well. (e.g calert)