How to use 'instance' as url for webhook contact point

We use Prometheus metrics as datasource for Grafana Alerting on a Java/Spring Boot application which consumes Kafka Messages. I’ve created an alert that triggers when the rate of Kafka exceptions is above a certain level.
I’d like to create a contact point that uses the instance from the alert as the webhook URL; such to instruct our application to stop the consumption of messages.

How can i get hold of the instance variable in the webhook configuration?

In the image below i use a hardcoded IP adres, but since this is in a cluster i’d like to use the instance variable from the alert.

webhook

By now i’ve learned that
https://{{index .CommonLabels “instance”}}/kafkacontrol
appears to do the job.
(and that what i called ‘variable’ is named ‘label’).