<?php

class ShippingEasy_Cancellation extends ShippingEasy_Object
{  
  
  public function __construct($external_order_identifier) {
    $this->$external_order_identifier = $external_order_identifier;
  }
  
  public function create()
  {
    $this->request("post", "/api/orders/$this->external_order_identifier/cancellations");
  }
  
}
<?php

class ShippingEasy_Cancellation extends ShippingEasy_Object
{  
  public function create($external_order_identifier)
  {
    $this->request("post", "/api/orders/$external_order_identifier/cancellations");
  }
  
}
--- 
+++ 
@@ -2,9 +2,14 @@
 
 class ShippingEasy_Cancellation extends ShippingEasy_Object
 {  
-  public function create($external_order_identifier)
+  
+  public function __construct($external_order_identifier) {
+    $this->$external_order_identifier = $external_order_identifier;
+  }
+  
+  public function create()
   {
-    $this->request("post", "/api/orders/$external_order_identifier/cancellations");
+    $this->request("post", "/api/orders/$this->external_order_identifier/cancellations");
   }
   
 }
Switch to passing in attrs in constructor.
