The underlying connection was closed: An unexpected error occurred on a send

I am trying to use DoDirectPayment method in my website.

This is the sample I am referring:

using com.paypal.sdk.services;
using com.paypal.sdk.profiles;
using com.paypal.sdk.util;
using com.paypal.soap.api;

namespace ASPDotNetSamples
{
    public class DoDirectPayment
    {
        public DoDirectPayment()
        {
        }
        public string DoDirectPaymentCode(string paymentAction, string amount, string creditCardType, string creditCardNumber, string expdate_month, string cvv2Number, string firstName, string lastName, string address1, string city, string state, string zip, string countryCode, string currencyCode)
        {

            com.paypal.soap.api.DoDirectPaymentReq req = new com.paypal.soap.api.DoDirectPaymentReq();


            NVPCallerServices caller = new NVPCallerServices();
            IAPIProfile profile = ProfileFactory.createSignatureAPIProfile();

            // Set up your API credentials, PayPal end point, API operation and version.
            profile.APIUsername = "sdk-three_api1.sdk.com";
            profile.APIPassword = "xxxxxxxxxxxxx";
            profile.APISignature = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
            profile.Environment = "sandbox";
            caller.APIProfile = profile;

            NVPCodec encoder = new NVPCodec();
            encoder["VERSION"] = "51.0";
            encoder["METHOD"] = "DoDirectPayment";

            // Add request-specific fields to the request.
            encoder["PAYMENTACTION"] = paymentAction;
            encoder["AMT"] = amount;
            encoder["CREDITCARDTYPE"] = creditCardType;
            encoder["ACCT"] = creditCardNumber;
            encoder["EXPDATE"] = expdate_month;
            encoder["CVV2"] = cvv2Number;
            encoder["FIRSTNAME"] = firstName;
            encoder["LASTNAME"] = lastName;
            encoder["STREET"] = address1;
            encoder["CITY"] = city;
            encoder["STATE"] = state;
            encoder["ZIP"] = zip;
            encoder["COUNTRYCODE"] = countryCode;
            encoder["CURRENCYCODE"] = currencyCode;

            // Execute the API operation 开发者_开发技巧and obtain the response.
            string pStrrequestforNvp = encoder.Encode();
            string pStresponsenvp = caller.Call(pStrrequestforNvp);

            NVPCodec decoder = new NVPCodec();
            decoder.Decode(pStresponsenvp);
            return decoder["ACK"];

        }
    }
}

This is the link:

https://cms.paypal.com/cms_content/US/en_US/files/developer/nvp_DoDirectPayment_cs.txt

When I pass appropriate parameter and try to run the code I get this error: "The underlying connection was closed: An unexpected error occurred on a send." on line:

pp_response = (DoDirectPaymentResponseType)caller.Call("DoDirectPayment", pp_Request);

The SOAP service call is inside the dll. Can anybody guide me what is happening and how to resolve it?

That is because that sample seems to be outdated, read up more on the stuff here:

• https://www.x.com/developers/paypal/sandbox
• https://www.x.com/developers/api-endpoints
• https://www.x.com/developers/paypal/documentation-tools/api