After processing a purchase with IAP, Apple may return SKError.Code.unknown. This is not reproduced in the Sandbox environment. https://developer.apple.com/documentation/storekit/skerror/code/unknown The documentation says "When this error occurs in production, it may indicate a problem with the user's iTunes account." However, due to the frequency of occurrence, I suspect there is another cause. Customer devices that are experiencing this will return the same error no matter how many times they try. In the case of subscriptions, the modal by Apple of "You are currently on a subscription" is followed by the return of SKError.Code.unknown. The customer may have been billed, in which case we guide them to a refund. When I contacted DTS about this, the only thing they said was that they don't know the cause of the problem and would like me to reproduce it and send them a bug report. I am trying to reproduce the problem at hand, but have not been able to do so yet. I would like to know if anyone has any experience with this issue or has improved it.