While it used to be necessary with Authorize.net to do things, with PayPal it doesn't really require (for our purposes, your mileage may be different) from them other than that your stuff is set up. All it takes is to put some well-formatted information in the url:
string serverResponse;
WebResponse wResp = request.GetResponse( );
using ( Stream datStream = wResp.GetResponseStream( ) ) using ( StreamReader datSReader = new StreamReader( datStream ) ) serverResponse = datSReader.ReadToEnd( );
this.Response = HttpUtility.ParseQueryString(serverResponse);
IsSuccess = this.Response.Get( "RESULT" ) == "0"; if ( !IsSuccess ) MessageBox.Show( "RESULT != 0: RESULT = " + this.Response.Get Response.Get ("RESULT")); thetermpapers.org
return IsSuccess;
This code, in its form before it was changed, came straight from the guys at PayPal and made it much easier to manage transactions through a windows form app.