There are several reasons why a transaction may fail when your customer tries to pay with Klarna.
Billing country is not available
At the moment, Klarna products via Mollie are only available to customers in the EEA. A customer will not be able to use Klarna to pay if they enter a billing country that isn’t available.
Customer is declined by Klarna
Klarna holds the right to deny customers from using their payment method. Reasons for this include failing the credit check.
Your webshop isn’t using the Mollie Orders API