When does the SKPaymentTransaction.original.transactionIdentifier field change?

When I start a subscription with sandbox in my application, the SKPaymentTransaction.transactionIdentifier changes while the SKPaymentTransaction.original.transactionIdentifier field always returns the same value. When I try to subscribe again after the subscription is canceled, it returns the same value. Does this field always return the same value? Does it change in renewals, upgrades or subscription downgrades?

Can you please tell me when this field changed?

Reference: https://developer.apple.com/documentation/storekit/skpaymenttransaction/1411284-original