diff --git a/src/Message/PurchaseRequest.php b/src/Message/PurchaseRequest.php
index 1619238..bc3f798 100644
--- a/src/Message/PurchaseRequest.php
+++ b/src/Message/PurchaseRequest.php
@@ -21,7 +21,7 @@ class PurchaseRequest extends AbstractRequest
      */
     public function getData()
     {
-        $this->validate('checkoutId', 'signKey', 'amount', 'currency', 'description', 'transactionId');
+        $this->validate('checkoutId', 'amount', 'currency', 'description', 'transactionId');
 
         $return = [
             'ik_co_id'          => $this->getCheckoutId(),