As per this documentation
A server URL to receive update notifications (JSON object posts) for key subscription events. This is applicable only for apps containing auto-renewable subscriptions. It is recommended to use these notifications in conjunction with Receipt Validation to validate users' current subscription status and provide them with service
We have added the URL but while checking the server log the link is not pinged,
Q1 - Is there any additional setup I need to do to test it in the sandbox?
Q2 - Is it only work for real purchase made by the user on production?
Q3 - Should I need to push an update to app store to make the Subscription URL work?
Any suggestion will be helpfull