The new tie-up with Stripe gives Klarna a big boost at a time when it's gearing up for a hotly anticipated initial public offering. Klarna confidentially filed to IPO in the United States in November. The company could fetch a valuation of as much as $20 billion, according to a Bloomberg News report out last year.

Klarna makes money from the fees that retailers pay on each transaction processed through its platform. In return for giving Klarna visibility as a payment option in its checkout tools, Stripe will get a share of the money Klarna makes from a given transaction.