Unable to test my C# code for make payment with credit card from my website

[paullejoy]

unable to make payment with my c# code unable to make connect with paypal sdk when i m try to test my code its show me error (Transaction Error: Error: This transaction cannot be processed. The merchant's account is not able to process transactions.) 10548 this is my code plz check 

string hostname = Dns.GetHostName();
string ip = Dns.GetHostByName(hostname).AddressList[0].ToString();
//API Credentials (3-token)
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;
string strUsername = "paullejoy9_api1.gmail.com";
string strPassword = "L7D2LYC3UTJCCUKD";
string strSignature = "A9LC3Qajo-H2V8mPq4eIktgPvG2RAu7RtQ5xuZR7cmasgxV8VCgG76AN";
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=" + ddlcardtype.Value
+ "&ACCT=" + txtcardno.Value
+ "&EXPDATE=" + ddlexpmonth.Value + ddlexpyear.Value
+ "&CVV2=" + txtcvv.Value
+ "&AMT=1" +
"&FIRSTNAME=" + txtfname.Value +
"&LASTNAME=" + txtlastName.Value +
"&IPADDRESS=" + ip +
"&STREET=" + txtstreet.Value +
"&CITY=" + txtcity.Value +
"&STATE=" + txtstate.Value +
"&COUNTRY=" + ddlcountry.Value +
"&ZIP=" + txtzipcode.Value +
"&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")
{
resultDiv.Visible = true;
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.";
lblstatus.Text = strSuccess;
}
else
{
resultDiv.Visible = true;
string strErr = "Error: " + htResponse["L_LONGMESSAGE0"].ToString();
string strErrcode = "Error code: " + htResponse["L_ERRORCODE0"].ToString();
lbltransactionerror.Text = strErr;
lblstatus.Text = strErrcode;
return;

}