Assuming that license related files in the repo are accurate this doesn't look all that complicated.

The License and notice files appear to be sufficient to understand the situation and there's really not a lot going on. The licensing files indicate that Klarna AB holds copyrights in the code (with some others mentioned) and that it is all licensed under Apache 2.0.

Naturally, the license related files in the repo can be inaccurate or incomplete. But when dealing with open source software you have to pick a point where you're going to trust these kinds of representations from strangers.

The code is released under the Apache-2.0 license. Doesn't seem complicated to me at all.