STOCKHOLM—Klarna said it will become the exclusive buy-now-pay-later provider at Walmart in the U.S., replacing rival Affirm as the Swedish fintech company nears a potential initial public offering.Stockholm-based Klarna said Monday that it will work with Walmart-backed consumer finance app OnePay to offer customers installment loans on purchases at the retailer.

Affirm shares are tumbling after rival Klarna, which is preparing to go public in the U.S., said it is now the exclusive provider of Buy Now, Pay Later loans for Walmart.

Klarna Group Plc is partnering with Walmart Inc.-backed OnePay to offer buy-now-pay-later to US shoppers, replacing Affirm as the retail giant’s fast credit option. Most Read from BloombergICE Eyes Massive California Tent Facility Amid Space ConstraintsHow Britain’s Most Bike-Friendly New Town Got BuiltThe Dark Prophet of Car-Clogged CitiesWashington,