We recently started using Offer Codes for a promotion of our app. However, some of our customers reported they were not able to use our premium services when they signed in our app, although their subscription succeeded completely in App Store. Since It seems like the following error occurred then, our app didn't call API on our server-side app to verify the receipt and the user wasn't recognized as the new subscriber.
Error Domain=ASDServerErrorDomain Code=3532
As our app checks the latest transaction only which is sent from SKPaymentTransactionObserver before asking the server-side to verify the receipt, we don't understand why the observer doesn't return the state of SKPaymentTransactionStatePurchased, but SKPaymentTransactionStateFailed even though the user's most recent subscription succeeded. In addition, the user say it has never subscribed our app before it used the offer code.
We'd like to know why it occurs sometimes and whether there is any workaround for this, or could we verify the receipt in case of the error code 3552 even if it's an error?