Whether the Klarna Checkout API documentation depends on a merchant's country or on a buyer's country?

As I see, Klarna Checkout API has different documentation for USA / United Kingdom and for other countries:

USA / United Kingdom employs Klarna Checkout version 3:

Other contries employ Klarna Checkout version 2:

Whether it depends on a merchant’s country or on a buyer’s country?

I have got an answer from Klarna support:

V3 is our based on a new server called Kasper, and is hosting our services for the UK and US.
It’s based on the buyers country.