I have the same issue .
The IAP works with iPhone iOS 14, but some other iPhone with iOS 13 system have the error. Tried some others method to check the issue ,but not work!!!
I found a lot of developers have the same issue, it may be the bug in iOS IAP sandbox environment.About some days before, IAP works fine.
ringren
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同样的问题：
Errors: (
"Error Domain=ITunesTransporterErrorDomain Code=1129 \"An error occurred saving your changes to the Apple database. This problem may be a transient issue on the Apple side. If the problem persists for more than an hour, please contact your iTunes representative. (1129)\" UserInfo={NSLocalizedRecoverySuggestion=An error occurred saving your changes to the Apple database. This problem may be a transient issue on the Apple side. If the problem persists for more than an hour, please contact your iTunes representative. (1129), NSLocalizedDescription=An error occurred saving your changes to the Apple database. This problem may be a transient issue on the Apple side. If the problem persists for more than an hour, please contact your iTunes representative. (1129), NSLocalizedFailureReason=An error occurred saving your changes to the Apple database. This problem may be a transient issue on the Apple side. If the problem persists for more than an hour, please contact your iTunes representative. (1129)}"
)