For transaction processing, wouldn't a 1-3% margin be about the maximum achievable? That would translate to about 15 million dollars in potential profit against a 730 million loss.
As a private tech company I would assume that they are using the broadest possible definition of revenue.
Klarna pays the vendor immediately (with its credit line), and the user enters into a sort of debt contract with klarna.
Klarna's revenue is what it receives from the user.
It's a great business model when the interest rate is 0%.
Implying that transaction volume is on the order of $200 billion? No.
For perspective, Amazon's 2018 revenue is $230 billion.
Edit: not "most likely" - apparently they lost to the tune of $700M