Not sure if you still use the Klarna/Stripe integration at your current place, but curious to hear what went wrong. Could you email me at edwin@stripe.com?
I'm afraid I left that company and went to a big tech company. I think it was just a combination of it being a private beta product so support/engineering were fairly uninformed, difficulty getting support for things that were in between Stripe and Klarna's services (a bit of blaming each other), and the fact that the Klarna flow didn't really fit Stripe's charge flow, so in terms of tech the integration was nearly as complex as a direct Klarna integration (obviously still beneficial in terms of the business side).