I'm considering developing an app where users can create their own subscription plans by freely setting their prices, similar to YouTube's membership feature. I understand that in-app purchases must be used to unlock features within the app. With that in mind, I searched for APIs to enable this functionality but couldn't find relevant information. When I contacted Apple directly, they mentioned that they couldn't provide specific answers unless the app is under review. If anyone has knowledge about the following points, I would greatly appreciate your response: Is it possible to implement a feature similar to YouTube's membership using in-app purchase APIs? If it's not feasible with in-app purchases, is it allowed to use external payment services like Stripe?