How do I get the information returned in the IPN after a transaction in PayPal using ci_merchant library?

I am a newbie to codeigniter and so far I have been doing great in developing my first application. However, when I tried to integrate CI_MERCHANT library to the site I am getting redirected to paypal just fine and I can even complete the transaction successfully and get redirected to my website. However, I am stuck on how to verify the "hidden information" sent by paypal to my application in addition to extracting this information and posting it to the database.

in my controller I have this:

public function place_order($id=NULL){
    $this->merchant->load('paypal_express');


    $id=$this->session->userdata('id');
    $customer_id=$id;
    $rules=$this->order_m->rules_place_order;
    $this->form_validation->set_rules($rules);

    if ($this->form_validation->run() == FALSE) // validation hasn't been passed
    {
        $this->data['subview']='customer/order_view';
        $this->load->view('templates/header_customer');
        $this->load->view('customer/_layout_main',$this->data);
        $this->load->view('templates/footer_customer');


    }
    else // passed validation proceed to post success logic
    {
        // build array for the model


        $data=$this->order_m->array_from_order(array('topic_title','discipline','academic_level','type_of_service','paper_format','pages','no_of_sources','no_of_slides','paper_details','deadline','timezones'));
        $data['customer_id']=$id;
        $this->order_m->save_data($data);

            $this->db->where('customer_id',$id);
            //get the last inserted id
            $no=$this->db->insert_id();




                $settings=$this->merchant->default_settings();

                //payment for order
                $params = array(
                            'amount' => 100.00,
                            'currency' => 'USD',
                            'return_url' => 'http://localhost/customers/order/paypal',
                            'cancel_url' => 'http://localhost/customers/order'
                            );

                $response=$this->merchant->purchase($params);


        }
    }
 public function paypal(){
    var_dump($_GET);
    $this->merchant->load('paypal_express');
    $settings=$this->merchant->default_settings();
    $params = array(
                            'amount' => 100.00,
                            'currency' => 'USD',
                            );

    $response=$this->merchant->purchase_return($params);
    var_dump($response);
    if ($response->status() == Merchant_response::AUTHORIZED)
    {
        echo "status is AUTHORIZED";
    }
    if ($response->status() == Merchant_response::FAILED)
    {
        echo "status is FAILED";
    }
    if ($response->status() == Merchant_response::REDIRECT)
    {
        echo "status is REDIRECT";
    }
    if ($response->status() == Merchant_response::COMPLETE)
    {
        echo "status is COMPLETE";
    }
    if ($response->status() == Merchant_response::REFUNDED)
    {
        echo "status is REFUNDED";
    }

This redirects me successfully to paypal and I can complete the transaction. However, I am unable to proceed from here since I am a newbie to payment processing. Kindly point me in the right direction on how to: 1. Verify every transaction with paypal and be able to visualize and post this information to my database. 2. Compare the information I posted to the database prior to redirecting the customer to paypal with what I receive from paypal.

You need to call the purchase_return() method when the customer is sent to your return_url. This will confirm the transaction with PayPal.