There's no need for sarcasm. I've resolved sandbox issues this way when nothing else works – including the obvious step of deleting the app completely before installing a new build, which you're implying that the poster has somehow failed to bother trying.
Aidano101
Users receive reputation points by contributing quality content to the forums.
Posts include post and replies published on the forums.
Post authors can mark replies as Accepted to indicate successful solutions.
Apple Developer Forums admins can mark replies as Apple Recommended to indicate an approved solution
Last seen
User for
Post
Replies
Boosts
Views
Activity
Make sure you're using an SKProduct that has been retrieved via a StoreKit query immediately prior to making the purchase. Do not cache SKProducts, otherwise some users will get this error.