private void btnDonate_Click(object sender, System.EventArgs e)
{
    string url = "";
 
    string business     = "my@paypalemail.com";  // your paypal email
    string description  = "Donation";            // '%20' represents a space. remember HTML!
    string country      = "AU";                  // AU, US, etc.
    string currency     = "AUD";                 // AUD, USD, etc.
 
    url += "https://www.paypal.com/cgi-bin/webscr" +
        "?cmd=" + "_donations" +
        "&business=" + business +
        "&lc=" + country +
        "&item_name=" + description +
        "&currency_code=" + currency +
        "&bn=" + "PP%2dDonationsBF";
 
    System.Diagnostics.Process.Start(url);
}