Klarna can be integrated in a Shopify store via multiple different integrations (although it is generally recommended to not duplicate Klarna integrations, but rather have Klarna active in checkout only using a single integration), such as:
To check which Klarna integration is active in your store, go to your shop admin -> Settings -> Payments to review your store's active payments methods.
You can also review the names of Klarna payment methods in your store's checkout. The translated list of Klarna supported payment methods is available here. If Klarna is listed multiple times in checkout (e.g. Pay now with Klarna, Pay later with Klarna, and Finance with Klarna), the integration is not supported directly via Klarna, but rather supported by the integrating partner.
For Klarna as an alternative payment method, Klarna has 2 apps available for Shopify merchants:
If you don’t yet have Klarna API credentials for the direct, alternative payment method, you can sign up at http://klarna.com/business
Once you have received your Klarna API credentials, please follow these steps to activate Klarna in your Shopify store.