title: How to Implement Klarna payment gateway with Sylius?
body: <p>I have been trying to add klarna checkout gateway without any luck...
  I don't see Klarna Checkout in the Admin UI!</p>
  
  <p>No idea what I'm missing here but the way I understood it that all I have to do is install the gateway payment through composer then add the fields in the config.yml file</p>
  
  <p>Do I need to make KlarnaGatewayConfigurationType.php file? if yes then where should I add it and what else should I do?</p>
  
  <p><strong>These are the steps I followed:</strong> 
  Installed Klarna: <code>composer require klarna/checkout</code></p>
  
  <p>Then I added in <code>app\config\config.yml</code> this code:</p>
  
  <pre><code>payum:
      gateways:
          klarna_checkout:
              factory: klarna_checkout
              secret:  'required'
              merchant_id: 'required'
              terms_uri: ''
              checkout_uri: ''
              sandbox: true
  
  sylius_payment:
       gateways:
              klarna_checkout: klarna_checkout
  </code></pre>
  
  <p>The  <code>php bin/console payum:gateway:debug</code> gave me this:</p>
  
  <pre><code>Order of actions, apis, extensions matters 
  Found 3 gateways 
  
  offline (Payum\Core\Gateway): 
          ........................................................................
  
  klarna_checkout (Payum\Core\Gateway): 
          Actions: 
          Payum\Core\Bridge\Symfony\Action\GetHttpRequestAction 
          Payum\Core\Bridge\Symfony\Action\ObtainCreditCardAction 
          Sylius\Bundle\PayumBundle\Action\CapturePaymentAction 
          Sylius\Bundle\PayumBundle\Action\ExecuteSameRequestWithPaymentDetailsAction 
          Sylius\Bundle\PayumBundle\Action\ResolveNextRouteAction 
          Payum\Core\Action\CapturePaymentAction 
          Payum\Core\Action\AuthorizePaymentAction 
          Payum\Core\Action\PayoutPayoutAction 
          Payum\Core\Action\ExecuteSameRequestWithModelDetailsAction 
          Payum\Core\Bridge\Twig\Action\RenderTemplateAction 
          Payum\Core\Action\GetCurrencyAction 
          Payum\Core\Action\GetTokenAction 
          Payum\Klarna\Checkout\Action\AuthorizeRecurringAction 
          Payum\Klarna\Checkout\Action\AuthorizeAction 
          Payum\Klarna\Checkout\Action\NotifyAction 
          Payum\Klarna\Checkout\Action\StatusAction 
          Payum\Klarna\Checkout\Action\SyncAction 
          Payum\Klarna\Checkout\Action\ConvertPaymentAction 
          Payum\Klarna\Checkout\Action\Api\CreateOrderAction 
          Payum\Klarna\Checkout\Action\Api\UpdateOrderAction 
          Payum\Klarna\Checkout\Action\Api\FetchOrderAction 
  
          Extensions: 
          Sylius\Bundle\PayumBundle\Extension\UpdatePaymentStateExtension 
          Payum\Bundle\PayumBundle\Profiler\PayumCollector 
          Payum\Core\Extension\GenericTokenFactoryExtension 
          Payum\Core\Bridge\Psr\Log\LoggerExtension 
          Payum\Core\Bridge\Psr\Log\LogExecutedActionsExtension 
          Payum\Core\Extension\StorageExtension 
                  Storage: Payum\Core\Bridge\Doctrine\Storage\DoctrineStorage 
                  Model: Sylius\Component\Core\Model\Order 
          Payum\Core\Extension\StorageExtension 
                  Storage: Payum\Core\Bridge\Doctrine\Storage\DoctrineStorage 
                  Model: Sylius\Component\Core\Model\Payment 
          Payum\Core\Extension\EndlessCycleDetectorExtension 
  
          Apis: 
          Payum\Core\Bridge\Httplug\HttplugClient 
          Payum\Klarna\Checkout\Config 
  
  Offline (Payum\Core\Gateway): 
          ........................................................................
  </code></pre>
  
  <p>Last step: <code>php bin/console cache:clear</code></p>
  
  <p>What am I doing wrong here?</p>