Example.swift

func refreshSubscriptionsStatus(callback : @escaping SuccessBlock, failure : @escaping FailureBlock){
        // save blocks for further use
        self.refreshSubscriptionSuccessBlock = callback
        self.refreshSubscriptionFailureBlock = failure
        guard let receiptUrl = Bundle.main.appStoreReceiptURL else {
                refreshReceipt()
                // do not call block yet
                return
        }
        #if DEBUG
            let urlString = "https://sandbox.itunes.apple.com/verifyReceipt"
        #else 
            let urlString = "https://buy.itunes.apple.com/verifyReceipt"
        #endif
        let receiptData = try? Data(contentsOf: receiptUrl).base64EncodedString()
        let requestData = ["receipt-data" : receiptData ?? "", "password" : self.sharedSecret, "exclude-old-transactions" : true] as [String : Any]
        var request = URLRequest(url: URL(string: urlString)!)
        request.httpMethod = "POST"
        request.setValue("Application/json", forHTTPHeaderField: "Content-Type")
        let httpBody = try? JSONSerialization.data(withJSONObject: requestData, options: [])
        request.httpBody = httpBody
        URLSession.shared.dataTask(with: request)  { (data, response, error) in
            DispatchQueue.main.async {
                if data != nil {
                    if let json = try? JSONSerialization.jsonObject(with: data!, options: .allowFragments){
                        self.parseReceipt(json as! Dictionary<String, Any>)
                        return
                    }
                } else {
                    print("error validating receipt: \(error?.localizedDescription ?? "")")
                }
                self.refreshSubscriptionFailureBlock?(error)
                self.cleanUpRefeshReceiptBlocks()                
            }
        }.resume()        
    }