Flutter - Implement IOS Subscription Offer to Desired Users

I want to provide a Subscription offer in my Flutter App for iOS devices. I have followed the IOS Subscription offer setup guides and I have the offer setup in Apple connect under the subscription.

I could not find any code officially maintained with in-app-purchase to use subscription code that is similar implementation to this.

https://developer.apple.com/documentation/storekit/in-app_purchase/original_api_for_in-app_purchase/subscriptions_and_offers/implementing_promotional_offers_in_your_app

This example does not have the Subscription offer. https://pub.dev/packages/in_app_purchase/example