         
         for product in products {
             if product.productIdentifier == art.productIdentifier {
+                
+                //4. Add product to the queue to purchase it
                 SKPaymentQueue.default().add(self)
                 let payment = SKPayment(product: product)
                 SKPaymentQueue.default().add(payment)

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


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)
