In-App purchase runs well in SandBox but rejected by review team - ios

Question

We have been rejected by review team recently for a In-App Purchase issue.
We discovered one or more bugs in your app when reviewed on iPhone
running iOS 8.2 on both Wi-Fi and cellular networks.
Specifically,
your application’s In App Purchase Transaction cannot be completed.
The steps to reproduce are:
Launch app
Navigate to purchase/recharge tab
Proceed to purchase one of the In-App Purchase products
In-App Purchase confirmation window appears
Confirm purchase
In-App Purchase results in an error
BUT! In-App Purchase runs well in sandbox! We checked log on our server, but we can't find any receipt verification logs. It seems that purchase completion window didn't appear at all.
We found we would use the following code sometimes:
SKPayment *payment = [SKPayment paymentWithProductIdentifier:productIdentifier];
[[SKPaymentQueue defaultQueue] addPayment:payment];
Is that the ONLY reason? T.T
EDIT:
We had released several versions before. This time we added a new product. But we forgot to add its identifier to the following array.
-(void)requestProducts
{
if (_products) {
return;
}
NSSet* identifiers = [NSSet setWithObjects:
#"identifier",
#"new identifier", // forgot this line
nil];
SKProductsRequest* _request = [[SKProductsRequest alloc] initWithProductIdentifiers:identifiers];
_request.delegate = self;
[_request start];
_requestProcessing = YES;
}
So the following code will return nil:
-(SKProduct*)getProduct:(NSString *)identifier
{
if (_products) {
for (SKProduct* product in _products) {
if ([product.productIdentifier isEqualToString:identifier]) {
return product;
}
}
} else if (!_requestProcessing) {
[self requestProducts];
}
return nil;
}
When user buy a product:
-(void)buyProductIdentifier:(NSString *)productIdentifier
{
if (![self isNetworkOK] || ![SKPaymentQueue canMakePayments]) {
[[NSNotificationCenter defaultCenter] postNotificationName:NotifyPurchaseFailed object:productIdentifier];
return;
}
NSLog(#"Buying %#...", productIdentifier);
SKProduct* product = [self getProduct:productIdentifier];
if (product) { // the new identifier gets nil here
SKPayment* payment = [SKPayment paymentWithProduct:product];
[[SKPaymentQueue defaultQueue] addPayment:payment];
} else { // calls the deprecated api
SKPayment *payment = [SKPayment paymentWithProductIdentifier:productIdentifier];
[[SKPaymentQueue defaultQueue] addPayment:payment];
}
}
BUT, it runs well in sandbox.
-(void)paymentQueue:(SKPaymentQueue *)queue updatedTransactions:(NSArray *)transactions
{
for (SKPaymentTransaction *transaction in transactions)
{
switch (transaction.transactionState)
{
case SKPaymentTransactionStatePurchased:
[self completeTransaction:transaction];
break;
case SKPaymentTransactionStateFailed: // may break here
[self failedTransaction:transaction];
break;
case SKPaymentTransactionStateRestored:
[self restoreTransaction:transaction];
default:
break;
}
}
}
Any idea? All the products on itunes connect are in Approved state except the new one. The new product is in Waiting for Review state.