IAPManager.swift

import UIKit
import StoreKit

class IAPManager: NSObject {
    static let shared = IAPManager()

    let PREMIUM_MONTH_PRODUCT_ID = "com.test.month"
    let PREMIUM_YEAR_PRODUCT_ID = "com.test.year"
    
    fileprivate var productsRequest = SKProductsRequest()
    fileprivate var iapProducts = [SKProduct]()

    // MARK: - FETCH AVAILABLE IAP PRODUCTS
    func fetchAvailableProducts(){
        productsRequest.cancel()
        // Put here your IAP Products ID's
        let productIdentifiers = NSSet(objects: PREMIUM_MONTH_PRODUCT_ID, PREMIUM_YEAR_PRODUCT_ID)
                
        productsRequest = SKProductsRequest(productIdentifiers: productIdentifiers as! Set<String>)
        productsRequest.delegate = self
        productsRequest.start()
    }
}

extension IAPManager: SKProductsRequestDelegate {
    // MARK: - REQUEST IAP PRODUCTS
    func productsRequest (_ request:SKProductsRequest, didReceive response:SKProductsResponse) {
        if response.products.count > 0 {
            iapProducts = response.products
            
            for product in iapProducts {
                print("productIdentifier - ", product.productIdentifier)
            }
        }
    }
    
    func request(_ request: SKRequest, didFailWithError error: Error) {
        print("Error load products", error)
    }
}