Follow this two link for more details
http://www.codeproject.com/Articles/19184/Use-of-the-PayPal-payment-system-in-ASP-NET
http://www.codeproject.com/Tips/474197/PayPal-Gateway-Integration-in-ASP-NET
http://www.mindstick.com/Articles/41de052a-37e1-41db-aa4c-123313be444a/?How%20to%20integrate%20PayPal%20in%20A
in config File write the following code
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http://www.codeproject.com/Articles/19184/Use-of-the-PayPal-payment-system-in-ASP-NET
http://www.codeproject.com/Tips/474197/PayPal-Gateway-Integration-in-ASP-NET
http://www.mindstick.com/Articles/41de052a-37e1-41db-aa4c-123313be444a/?How%20to%20integrate%20PayPal%20in%20A
in config File write the following code
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<appSettings>
<add key="token" value="PW1BDVNqVPVanwduF_Tb2Ey91aT1Uhx1kL7HPc-7e8S-6AnUwSSHyasolSe"/>
<add key="paypalemail" value="snehasish@gmail.com"/>
<!--Here i used sandbox site url only if you hosted in live change sandbox to live paypal URL-->
<add key="PayPalSubmitUrl" value="https://www.paypal.com/cgi-bin/webscr"/>
<add key="FailedURL" value="http://www.xyz.co.in/ProceedToPayment.aspx"/>
<add key="SuccessURL" value="http://www.xyz.co.in/ProceedToPayment.aspx"/>
</appSettings>
Write the code in the code behind page
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protected void PayWithPayPal(string amount, string itemInfo, string name,
string phone, string email, string currency)
{
string redirecturl = "";
//Mention URL to redirect content to paypal site
redirecturl += "https://www.paypal.com/cgi-bin/webscr?cmd=_xclick&business=" +
ConfigurationManager.AppSettings["paypalemail"].ToString();
//First name i assign static based on login details assign this value
redirecturl += "&first_name=" + name;
//City i assign static based on login user detail you change this value
redirecturl += "&city=bhubaneswar";
//State i assign static based on login user detail you change this value
redirecturl += "&state=Odisha";
//Product Name
redirecturl += "&item_name=" + itemInfo;
//Product Name
redirecturl += "&amount=" + amount;
//Phone No
redirecturl += "&night_phone_a=" + phone;
//Product Name
redirecturl += "&item_name=" + itemInfo;
//Address
redirecturl += "&address1=" + email;
//Business contact id
// redirecturl += "&business=k.tapankumar@gmail.com";
//Shipping charges if any
redirecturl += "&shipping=0";
//Handling charges if any
redirecturl += "&handling=0";
//Tax amount if any
redirecturl += "&tax=0";
//Add quatity i added one only statically
redirecturl += "&quantity=1";
//Currency code
redirecturl += "¤cy=" + currency;
//Success return page url
redirecturl += "&return=" +
ConfigurationManager.AppSettings["SuccessURL"].ToString();
//Failed return page url
redirecturl += "&cancel_return=" +
ConfigurationManager.AppSettings["FailedURL"].ToString();
Response.Redirect(redirecturl);
}