We use grafana for alert configuration, which is based on conversion rate.
The data source of grafana is ES (Elasticsearch).
First set up 2 queries in query,
buyCnt: Number of page button clicks.
pageCnt: is the number of page impressions
Conversion via Expression: rate = $buyCnt / $pageCnt.
In the alert, set the alarm according to the rate, and prompt an error: The datasource does not support alerting queries