introductoryPrice property

The object represents the duration of single subscription period.

This is only available if you set up the introductory price in the App Store Connect, otherwise the value is null. Programmer is also responsible to determine if the user is eligible to receive it. See https://developer.apple.com/documentation/storekit/in-app_purchase/offering_introductory_pricing_in_your_app?language=objc for more details. The subscriptionPeriod of the discount is independent of the product's subscriptionPeriod, and their units and duration do not have to be matched.