             for product in self.products {
                 if product.productIdentifier == art.productIdentifier {
                     
+                    //3. Show products for purchase
                     let formatter = NumberFormatter()
                     formatter.numberStyle = NumberFormatter.Style.currency
                     formatter.locale = product.priceLocale

        self.collectionView.reloadData()
    }
    
    func paymentQueue(_ queue: SKPaymentQueue, updatedTransactions transactions: [SKPaymentTransaction]) {
        for transaction in transactions {
            switch transaction.transactionState {


extension ViewController: SKProductsRequestDelegate, SKPaymentTransactionObserver {
    
    // 1. Request products
    func requestProducts() {
        let IDs: Set<String> = ["com.gethomeworktutor.TheGallery.tigerart",  "com.gethomeworktutor.TheGallery.natureart"]
        let productsRequest = SKProductsRequest(productIdentifiers: IDs)
