What? Isn’t revenue kind of … revenue? What else can it be?

To my knowledge, there isn't any reason klarna can't describe their transaction volume as revenue. Then declare their margin 3%.

As a private tech company I would assume that they are using the broadest possible definition of revenue.

No. GAAP and IFRS have very strict definitions of Revenue. Transaction volume falls under the agency principle. Its not the Co's revenue.

That's not what a klarna transaction is.

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%.

Dunno about Sweden but lots of compensation stuff triggers financial reporting requirements for obvious reasons.