I don't think they are a lending company. They do not charge interest, their model lets you pay over time, and you pay a fixed fee to extend the payments. It's all fee based, no interest, so i think there's some regulations they get to sidestep.
You can call it a fee, or a surcharge, but in the end it's principal + interest for deviating from a schedule.
Klarna Bank AB is a bank, providing credit and charging interests, it got its bank licence from Finansinspektionen around 2017-2018.