Paypal showing , Error Detected The Cart is Empty

[eluser]fnbhns[/eluser]
Hi Friends,

I am trying to integrate paypal with my site for single item. Its showing message "Error Detected The CART is empty". But whats the steps should i follow i am really not understanding, Need your kind support, if you give me support the steps, i am ready to do it newly.

Some code detail given below

Controller :

Code:

<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
class Paypal extends CI_Controller{

function __construct(){
parent::__construct();
$this->load->library( 'Paypal_Lib' );
$this->load->library('cart');

}

function index(){
$this->load->view('payment');
}

function pay(){

            $item_name = 'Sun Glass';
            $price = '50';
            $item_id = '001';  //'Product Id'
            $quantity = 1;

            $this->paypal_lib->add_field('business','[email protected]'); // Business Email
            $this->paypal_lib->add_field('return',base_url().'returnpage'); // Return URL          
            $this->paypal_lib->add_field('cancel_return', base_url().'cancel'); // Cancel URL          
            $this->paypal_lib->add_field('notify_url', base_url().'ipn'); // <-- IPN url
            $this->paypal_lib->add_field('custom', $item_id);  // Optional
            $this->paypal_lib->add_field('item_name', $item_name); // Product Name
            $this->paypal_lib->add_field('quantity', $quantity); // Quantity
            $this->paypal_lib->add_field('amount', $price); // Price
            
            $this->paypal_lib->paypal_auto_form();

}

function returnpage(){

            if(!$this->input->post('payer_id')){
            echo "Success !!";
            }else{
            echo "Error !!";
            }

}

function cancel(){
            redirect(base_url().'paypal');
}

function ipn(){

            $to    = '[email protected]';

            if ($this->paypal_lib->validate_ipn()) {

            $body  = 'An instant payment notification was successfully received from ';
            $body .= $this->paypal_lib->ipn_data['payer_email'] .
            ' on '.date('m/d/Y') . ' at ' . date('g:i A') . "nn";
            $body .= " Details:n";

            foreach ($this->paypal_lib->ipn_data as $key=>$value)
            $body .= "n$key: $value";

           $this->load->library('email');
            $this->email->to($to);
            $this->email->from($this->paypal_lib->ipn_data['payer_email'],
            $this->paypal_lib->ipn_data['payer_name']);
            $this->email->subject('Received Payment');
            $this->email->message($body);
            $this->email->send();

            }
}

}

The Libraries is Paypal_Lib :

Code:

class Paypal_Lib {

var $last_error;  
var $ipn_log;    
var $ipn_log_file;  
var $ipn_response;    
var $ipn_data = array();
var $fields = array();  
var $submit_btn = '';  
var $button_path = '';  

var $CI;

function Paypal_Lib()
{
  $this->CI =& get_instance();
  $this->CI->load->helper('url');
  $this->CI->load->helper('form');
  $this->CI->load->config('paypallib_config');
  
  $this->paypal_url = 'https://www.sandbox.paypal.com/cgi-bin/webscr';
  $this->last_error = '';
  $this->ipn_response = '';
  
  $this->ipn_log_file = $this->CI->config->item('paypal_lib_ipn_log_file');
  $this->ipn_log = $this->CI->config->item('paypal_lib_ipn_log');                   $this->button_path = $this->CI->config->item('paypal_lib_button_path');    

  $this->add_field('rm','2');    
  $this->multi_items('true');

  $this->add_field('currency_code', $this->CI->config->item('paypal_lib_currency_code'));
             //$this->add_field('quantity', '1');
  $this->button('Pay Now!');
  
}

function button($value)
{
  // changes the default caption of the submit button
  $this->submit_btn = form_submit('pp_submit', $value);
}

function image($file)
{
  $this->submit_btn = '<input type="image" name="add" src="' . site_url($this->button_path .'/'. $file) . '" border="0" />';
}


function add_field($field, $value)
{
  $this->fields[$field] = $value;
  //print_r($this->fields);
}

function paypal_auto_form()
{
  $this->button('Click here if you\'re not automatically redirected...');
                 echo  '<html>' . "\n";
  echo '<head><title>Processing Payment...</title></head>' . "\n";
  echo '<body >' . "\n";
  echo '<p>Please wait, your order is being processed and you will be redirected to the paypal website.</p>' . "\n";
  echo $this->paypal_form('paypal_auto_form');
  echo '&lt;/body&gt;&lt;/html>';
  
}

  paypal_form($form_name='paypal_form')
{
  $str = '';
  $str .= '&lt;form method="post" acti name="'.$form_name.'"/&gt;' . "\n";
  foreach ($this->fields as $name => $value)
  $str .= form_hidden($name, $value) . "\n";
  $str .= '<p>'. $this->submit_btn . '</p>';
  $str .= form_close() . "\n";
  return $str;
}
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Some other code is there

If your require any more information please let me know. Even if you give me support the steps, i am ready to do it newly these paypal.Thanking you in advance for your help. Looking forward.