Paypal NVP API example in C# (asp.net)

This API is a very easy way to accept credit cards through your web app. Although , I don't think there are any simple examples available for ASP.Net 2.0. This beginner example will at least allow you to send a request to paypal and then get the response back from the API and display the error to a label.

Prereqs:
- Paypal business account with paypal websites pro enabled
- Paypal sandbox account (you must login and accept the agreement for websites pro from this account)
- get an API username, password, & signature from your sandbox account

Steps:
1- create an ASPX form with the following fields:
cctypeDdl, ccnumberTextbox, expdateDropDown, yearDropDown, CVVcodeTextBox, amountTextBox, firstnameTextbox, lastnameTextbox, addressTextbox, cityTextbox, regionTextbox, countryDropDown, postalTextbox
and these labels: successLabel, errLabel, errcodeLabel

2- Create a button control and button_click event handler

3- copy below code into your event handler

//API Credentials (3-token)
string strUsername = "brad_apiX.w3XXXXX.com";
string strPassword = "XXXCCGUJP2EXXXX";
string strSignature = "XXXXXXZLVYanEw944w0oPBsJXXXXXXX";
string strCredentials = "USER=" + strUsername + "&PWD=" + strPassword + "&SIGNATURE=" + strSignature;

string strNVPSandboxServer = "https://api-3t.sandbox.paypal.com/nvp";
string strAPIVersion = "2.3";

string strNVP = strCredentials + "&METHOD=DoDirectPayment" +
"&CREDITCARDTYPE=" + cctypeDdl.Text +
"&ACCT=" + ccnumberTextbox.Text +
"&EXPDATE=" + expdateDropDown.Text + yearDropDown.Text +
"&CVV2=" + CVVcodeTextBox.Text +
"&AMT=" + amountTextBox.Text +
"&FIRSTNAME=" + firstnameTextbox.Text +
"&LASTNAME=" + lastnameTextbox.Text +
"&IPADDRESS=255.55.167.002" +
"&STREET=" + addressTextbox.Text +
"&CITY=" + cityTextbox.Text +
"&STATE=" + regionTextbox.Text +
"&COUNTRY=" + countryDropDown.Text +
"&ZIP=95110" + postalTextbox.Text +
"&COUNTRYCODE=US" +
"&PAYMENTACTION=Sale" +
"&VERSION=" + strAPIVersion;

try
{
//Create web request and web response objects, make sure you using the correct server (sandbox/live)
HttpWebRequest wrWebRequest = (HttpWebRequest)WebRequest.Create(strNVPSandboxServer);
wrWebRequest.Method = "POST";
StreamWriter requestWriter = new StreamWriter(wrWebRequest.GetRequestStream());
requestWriter.Write(strNVP);
requestWriter.Close();

// Get the response.
HttpWebResponse hwrWebResponse = (HttpWebResponse)wrWebRequest.GetResponse();
StreamReader responseReader = new StreamReader(wrWebRequest.GetResponse().GetResponseStream());

//and read the response
string responseData = responseReader.ReadToEnd();
responseReader.Close();

string result = Server.UrlDecode(responseData);

string[] arrResult = result.Split('&');
Hashtable htResponse = new Hashtable();
string[] responseItemArray;
foreach (string responseItem in arrResult)
{
responseItemArray = responseItem.Split('=');
htResponse.Add(responseItemArray[0], responseItemArray[1]);
}

string strAck = htResponse["ACK"].ToString();

if (strAck == "Success" || strAck == "SuccessWithWarning")
{
string strAmt = htResponse["AMT"].ToString();
string strCcy = htResponse["CURRENCYCODE"].ToString();
string strTransactionID = htResponse["TRANSACTIONID"].ToString();
ordersDataSource.InsertParameters["TransactionID"].DefaultValue = strTransactionID;

string strSuccess = "Thank you, your order for: $" + strAmt + " " + strCcy + " has been processed.";
successLabel.Text = strSuccess;
}
else
{
string strErr = "Error: " + htResponse["L_LONGMESSAGE0"].ToString();
string strErrcode = "Error code: " + htResponse["L_ERRORCODE0"].ToString();
errLabel.Text = strErr;
errcodeLabel.Text = strErrcode;
return;
}
}
catch (Exception ex)
{
// do something to catch the error, like write to a log file.
Response.Write("error processing");
}

Keep in mind that you'll need to serve this page via SSL for production use. Otherwise, someone could sniff all your customers credit card numbers. For a inexpensive SSL certs, try godaddy.com