Follow these steps to enable Server Notifications v2 for your app in App Store Connect:
Log into your App Store Connect here.
Select your app.
Navigate to App information.
Scroll down to the App Store Server Notifications section and click Edit next to Production Server URL.
In a popup window select Version 2 Notifications and click Save.
⚠️ Important: If your URL is in use, make sure the service listening to notifications is updated to support Version 2.