I have also tried all event but didn't get success. Then I moved to override Mage OnePageController and called my custom function. Below is the code to override onestep checkout.
app\etc\modules\Namespace_Module.xml
<Namespace_Checkout>
<active>true</active>
<codePool>local</codePool>
</Namespace_Checkout>
app\code\local\Namespace\Checkout\etc\config.xml
<?xml version="1.0"?>
<config>
<modules>
<Namespace_Checkout>
<version>0.1.0</version>
</Namespace_Checkout>
</modules>
<frontend>
<routers>
<checkout>
<args>
<modules>
<Namespace_Checkout before="Mage_OneStepCheckout">Namespace_Checkout</Namespace_Checkout>
</modules>
</args>
</checkout>
</routers>
</frontend>
</config>
app\code\local\Namespace\Checkout\controllers\OnepageController.php
<?php
require_once 'Mage/Checkout/controllers/OnepageController.php';
class Namespace_Checkout_OnepageController extends Mage_Checkout_OnepageController{
public function successAction(){
$session = $this->getOnepage()->getCheckout();
if (!$session->getLastSuccessQuoteId()) {
$this->_redirect('checkout/cart');
return;
}
$lastQuoteId = $session->getLastQuoteId();
$lastOrderId = $session->getLastOrderId();
$lastRecurringProfiles = $session->getLastRecurringProfileIds();
if (!$lastQuoteId || (!$lastOrderId && empty($lastRecurringProfiles))) {
$this->_redirect('checkout/cart');
return;
}
$this->customFunction(); // Custom function to call
$session->clear();
$this->loadLayout();
$this->_initLayoutMessages('checkout/session');
Mage::dispatchEvent('checkout_onepage_controller_success_action', array('order_ids' => array($lastOrderId)));
$this->renderLayout();
}
function customFunction(){
// This function is calling before clearing order session
//Here you can put all your custom code
}
}
?>
In the above controller, I have added customFunction()
wher you can put your custom code.
Hope it will help you!