Don't waste your time.
First, they give you an IQ test. If you pass it, you also get a task in your preferred programming language.
What I got as feedback for being rejected:
'Code formatting and spaces is bad' - (You are forced to use a web interface which does not format the code). Additionally, it's 2019, and usually, code is formatted automatically.
'Two of the solutions were copied and modified from Google' - You are not notified that you should not use Google and reinvent the wheel, and tasks are pretty basic, so chances are you will end up 'copying the solution'.
IQ Test
Basic coding challenge
The following metrics were computed from 1 interview experience for the Klarna Software Engineer role in Finland.
Klarna's interview process for their Software Engineer roles in Finland is extremely selective, failing the vast majority of engineers.
Candidates reported having very negative feelings for Klarna's Software Engineer interview process in Finland.