What fields are available to customise Grafana SLO Slack messages?

We’re using Grafana SLO with Slack alerting and the messages aren’t quite how we want them and they provide the wrong URL when clicked upon (not linking back to the dashboard).

We started working on customising the alerts, however this just seemed to stop them and we can’t find out what the available fields are in order to write the templates.

With the external event manager, we unfortunately don’t get the test message UI

Is it possible to get a list of available fields that can be used when creating a template?

Thanks