My payment has been rejected. What can I do?
When purchasing on account, you will be subjected to a credit check on our behalf by a credit agency commissioned by Unzer E-Com GmbH. Unfortunately, we have no way of influencing this process. In the event of a failed order, you should always first check whether the account details provided were correct or whether the credit or debit card may have expired. To try a different payment method, you do not have to place a new order, but can simply change the payment method in your existing order. If necessary, please also contact your bank to clarify the matter.
https://www.siku.de/en/Frequently-asked-questions/Onlineshop/My-payment-has-been-rejected.-What-can-I-do