How “Subscription Status Url” works for apple In-a

Question

Does anybody work on "Subscription Status Url" and how it works for Auto Renewable In-app purchases in the sandbox mode

When i am trying to achive it, i am able to subscribe my product from App but while checking subscription status in the backend (server) we are not getting any "statusUpdateNotifications" from Apple Server. We have tested our URL and it is as per Apple security norms.

We went through below link but didn't get much information

Working with Subscriptions