The unique identifier for the subscription.
- iOS 8.0+
- macOS 10.10+
- Mac Catalyst 13.0+Beta
- tvOS 9.0+
- watchOS 6.0+Beta
If you initialize the subscription object using the
init methods, the default value of this property is set to the value provided by those methods. In all other cases, an ID based on a UUID is generated for you automatically.