Klarna is a payment provider similar to Paypal, and offers both an online payment and purchase on invoice ("pay in 4").
Simply select "Klarna" as your payment method - you can decide in the next step which variant you would like to choose.
No fees are charged to the buyer. Please note that on your invoice, the "CSL Computer Service Langenbach GmbH" will be named.
For more details see Klarna.com.