We are building a delivery grocery app. The physical goods are payed without an IAP system but by our own payment system(and that fine according the guidelines). But we want also to provide a subscription system where we can offer free delivery. At the moment the user subscribed there some visuals in the app that will change(like a button to go your subscription information, canceling the subscription, modify your subscription). Are we still safe to use our own subscription system, without using StoreKit(and 30% commission)? Or will we be rejected when the app is reviewed by Apple?