So 2 years after this question : You've already purchase this subscription. Tap Buy to renew or extend it
I'm still seeing that when renewing a non auto renewing subscription that the user get's 2 "Buy" dialogs even if the subscription is already expired:
First dialog: "Confirm your In-App Purchase"
Second dialog (after clicking Buy on the first one): "You've Already Purchased This Subscription, Tap Buy to renew or extend it".
Is there really no way to avoid this? I'm testing in the sandbox right now but no reason to think it is different in production. User can now end up with 3 dialog boxes (1 to enter password for App Store, then the 2 dialogs).