Error when creating a credit memo for order with payment method Klarna After Pay

[gjportegies]

Describe the bug When creating a credit memo, for an order with payment method Klarna After Pay, we're getting a hard error with the following message:

[2023-02-06 13:04:03] main.CRITICAL: You can not refund shipping if there is no shipping amount. {"report_id":"<report-id>","exception":"[object] (Magento\\Framework\\Exception\\LocalizedException(code: 0): You can not refund shipping if there is no shipping amount. at /<path-to-webshop>/vendor/magento/module-sales/Model/Order/Creditmemo/Total/Discount.php:62)"} []

Used versions

• Magento Version number(eg 2.3.5): 2.4.3-p3
• Open source/Enterprise/B2b: Open source
• Mollie version number (Check configuration): 2.21.0

To Reproduce Steps to reproduce the behavior:

1. Go to Sales -> Order Grid
2. Open a completed order with the payment method Klarna After Pay.
3. Try to create a credit memo.
4. See error

Expected behavior A credit memo should be created.

Actual behavior An error is thrown.

Screenshots If applicable, add screenshots to help explain your problem.

Additional context Lately we've experienced a lot of issues with Klarna payment methods (both Klarna Pay Later and Klarna Slice It).

• We've had approx. 500 orders that were cancelled multiple times (https://github.com/mollie/magento2/issues/500). For those orders there were double records in the 'inventory_reservation' table that caused the salable_qty to be higher than the qty. Customers could order products that were not available.
• We've orders with multiple invoices as mentioned in this issue https://github.com/mollie/magento2/issues/605

[Frank-Magmodules]

Hi @gjportegies , based on our investigation, this issue also appears to be related to the webhook firing faster than before, which results in an update before the order is saved into Magento and seems to created extra order lines as result. 

To address this, we have implemented a solution that involves appending an encrypted order ID to the webhook URL. This will serve as a fallback in situations where the transaction ID is not found in Magento.

In such cases, we will compare the order ID from the metadata in the loaded transaction on the Mollie side and set the transaction ID to the order to process the webhook. This will ensure that the order is properly processed and any necessary actions are taken. This solution is now available within our new [2.22.0](https://github.com/mollie/magento2/releases/tag/v2.22.0) release.

We understand the importance of timely and accurate order processing and appreciate your patience as we work to resolve this issue. Please let us know if you have any further questions or concerns.

We are closing this issue now but please feel free to reopen the issue if this still occurs.