i create observer for change shipping method amount but it does not worked. this is my code Cop/Postexpres/etc/events.xml

<?xml version="1.0"?><config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd"> <event name="sales_order_shipment_save_after">     <observer name="popopp" instance="Cop\Postexpres\Model\Observer"  /> </event> 

and `Cop/Postexpres/Model/Observer.php’

namespace Cop\Postexpres\Observer; 

use Magento\Framework\Event\ObserverInterface;

class Observer implements ObserverInterface {     public function execute(\Magento\Framework\Event\Observer $  observer)     {         echo 11111111;         die();          $  shipment = $  observer->getEvent()->getShipment();         $  order = $  shipment->getOrder();        var_dump($  order->getData());      }  }