In App Purchase invalidProductIdentifier in 30% times why ?

I've configured IAP for my project and It seems to work, so my app is live on app store but I've discovered that approximately 30% requests to iTunes returning invalidProductIdentifier for some reason, below is the complete code:

class IAP: NSObject, SKProductsRequestDelegate {

    static let sharedInstance = IAP()

    func productsRequest(request: SKProductsRequest, didReceiveResponse response: SKProductsResponse) {
        response.invalidProductIdentifiers.forEach() { id in
            //here is the part that could fail sometimes
            print(id)
        }
    }

    //here how I setup IAP
    func canMakePayments() {
        if(SKPaymentQueue.canMakePayments()) {
            var productID = NSSet()
            productID = NSSet(object: "unlock")
            let request: SKProductsRequest = SKProductsRequest(productIdentifiers: productID as! Set<String>)
            request.delegate = self
            request.start()
        }
    }
}

And here how I use it from AppDelegate:

func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
        IAP.sharedInstance.canMakePayments()
        return true
    }

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