@Rohan can you try something like this? I used a dummy test datasource and gave it one of your test labels with dots in the name. Then, I set the value of metadata.label.user.app to slack.
Then I set the custom label to a value of {{index $labels "metadata.label.user.app"}}
My default notification policy is email. To test that the label is working. I created a rule to route alerts with metadata.label.user.app=slack to my slack contact point overriding the default:
