Install app: Since only the full store account owner can install Shopify payments apps and activate payment methods in their store, make sure you are logged into your Shopify store as the store account owner. Click the "Install Klarna Shopify Application" button. (Note: while this app is a public app, it is not listed in the Shopify app store, and will not be displayed in your store's 'Apps'menu like other apps, which is standard for Shopify new payments apps).
Connect: Generate & connect new Klarna API credentials. As directed, for security purposes, download these API credentials to your local computer, even though you won't enter these credentials manually in this new payments integration flow as that is done automatically for you.
Test: the integration is verified. This step will do a verification API call automatically to confirm that your API credentials can successfully create a session for Klarna Payments with your store settings (e.g. store's base currency).
Activate: activate the new, single alternative payment method, named "Klarna", in your Shopify store admin (which is only permissible as the full account owner of the store). There may be other payment methods supporting Klarna available to activate, such as Paymentwall, pay.nl, etc., but those other payment methods require different credentials and different corresponding payments apps to work successfully. Activating a payment options other than the one named only "Klarna" will result in an error upon redirect from Shopify checkout without appropriate credentials. When the appropriate "Klarna" payment method is activated, "Klarna" will display as a payment method in your Shopify checkout, per screenshot below.
Verify: first add a product to your cart. Go through your Shopify checkout, select Klarna in the your store's checkout payment page, and after clicking the “Pay Now” or "Complete" button (or after the Review Order page, if configured for your store), simply make sure the Klarna hosted payment page loads successfully. Placing a test order as fees is not necessary, and be aware that fees could apply if the payment method isn't in "test mode".
(Note: initially, only the production merchant portal will be supported for test mode of the payment method; a production merchant account will be required even for test mode orders.)
Klarna is now live in your Shopify store!
Check out this video to see the new installation in action.