Not sure if this is the same issue but I've also run into the error 'Transaction id not found'. In my case it turns out I used the transactionId.formatted() function which adds dots to the string representation of the transaction Id, e.g. 2.000.000.123.123.123. The apple server can't find the transaction id formatted like that. So after switching to a regular string representation of the number using String(transaction.transactionId) it works fine.