Klarna's API relies on standard HTTP response codes to signal the success or failure of a request. When an API call is successful, Klarna will respond with a 2xx status code and when the API call fails Klarna will respond with a 4xx or 5xx status code together with a response body containing an error object with the error code, an array of error messages and a unique correlation id to be used to identify the request.
2xx codes indicate success.4xx codes indicate an an error on the client side (e.g., missing parameters or failed transactions).5xx codes indicate server-side errors.In order to deep dive on error make sure you check PSP logs dashboard or Klarna Developers Logs app in Merchant Portal for error messages to see what's exactly wrong in the details.