Error-Message after pay via E-mail

Hello,
we use Klarna Checkout for WooCommerce and the Plugin Germanized. We use the manual Conclusion of Contract. If the customer pays per Klarna, he receives an email with a Pay-now-Link. But if the customer click the Link, he come to the Checkoutpage. If he click the Pay-now-Button, the page stays on the same checkout-page and there is an error massage with HTTP_ERROR.
I’ve read there is a known issue with the manual Conclusion of Contract but after the customer completes the payment. In our case, the customer can’t complete the payment.