Query using Grafana for Managed Service for Prometheus issue

I currently made use of this [docs](https://cloud.google.com/stackdriver/docs/managed-prometheus/query#ui-grafana) to setup grafana getting query on Managed Service for Prometheus. I have done all the configuration in the docs but when I got to this part in the docs

`Go to your newly configured Grafana data source and verify the Prometheus server URL value starts with https://monitoring.googleapis.com. You might have to refresh the page. Once verified, go to the bottom of the page and select Save & test. You need to select this button at least once to ensure that label autocompletion in Grafana works.`

When I verified the Prometheus server URL value its not showing `https://monitoring.googleapis.com`.

The datasource-syncer was deployed properly