This guide explains how to integrate the Klarna Web SDK to (1) display Klarna as a payment option during checkout, (2) start the payment process, and (3) transfer authorization to Worldline. This flow is designed for one-time payment scenarios, where customers initiate payments directly from the Partner’s user interface.

This integration approach applies only when you build and control your own payment form within the checkout. It provides full ownership of the customer experience while Klarna delivers ready-made UI components to manage the payment interface.

​

Before you integrate, check that you meet the following prerequisites:

1. Ensure that you have Klarna enabled with Worldline.
2. Confirm you have access to the Klarna Portal.
3. Inside Klarna Portal:
   1. Confirm that you have generated a client identifier with your domain URL allowlisted.
   2. Confirm that you have generated an API key.
4. Confirm that you have registered webhooks for payment.request.state-change.completed events following Webhooks guidelines.
5. Add Terms and Conditions for Web SDK.

Here's an overview of all the steps to display Klarna and initiate payments via the WebSDK:

1. Present Klarna as a payment option in the payment form.
2. Customer clicks the Klarna payment button in your checkout.
3. You create a server-side payment request to Klarna and share available interoperability data points.
4. If customer interaction is required, Klarna returns a payment_request_id.
   1. The payment_request_id is used to initiate the purchase flow with Klarna’s WebSDK.
   2. The Klarna purchase journey is launched.
   3. The customer completes the Klarna purchase journey.
5. Klarna returns an interoperability_token via webhook.
6. You create an authorization request with Worldline and share the required interoperability data points.
7. Worldline responds with an approval and order completion.
8. Customer is redirected to your confirmation page.

Presenting Klarna in the payment form involves retrieving the visual assets, localized text, and display instructions required to correctly render Klarna as a payment option and display the payment button. This dynamic presentation ensures a consistent customer experience, accurate localization, and optimized conversion performance, while adapting seamlessly to different checkout states.

​On a high level, the process involves:

1. Initialize Klarna Web SDK in your checkout experience.
2. Request Klarna’s payment presentation for the current payment context.
3. Render Klarna payment option(s) dynamically in the payment form according to the instructions.
4. Allow the customer to select and deselect a Klarna payment option.
5. Display the Klarna button and start the payment process when clicked.

​The expected outcomes are as follows:
​

Initial presentation	When Klarna is selected

​

​

Initialize the Web SDK

The Klarna Web SDK (klarna.mjs) follows the JavaScript module approach and should be included in places where you need to have a reference to the SDK such as while rendering any components or initiating a payment flow. Here are the initialization parameters:

For the full API specifications, refer to Klarna Web SDK.
SDK initialization sample

<script type="module">
  const { KlarnaSDK } = await import("https://js.klarna.com/web-sdk/v2/klarna.mjs")

  const Klarna = await KlarnaSDK({ 
    clientId: "[client-id]",
    products: ["PAYMENT"],
    locale: "en-US", // optional
  })

  // Klarna SDK ready to be utilized
  // Klarna.Payment.button().mount('#payment_container')
</script>

Request payment presentation

Klarna payment presentation provides all the visual assets, localized texts, and instructions needed to correctly display Klarna in your checkout form.

Use the initialized SDK instance to call the Klarna.Payment.presentation() method.

Basic checkout context parameters must be provided:

For the full API specifications, refer to Klarna Web SDK.

Sample code

const paymentPresentation = await klarna.Payment.presentation({
  amount: 11800,
  currency: "USD",
  locale: "en-US",
  intents: ["PAY"] 
});

Render Klarna according to instructions

The PaymentPresentation interface provides the full Klarna branding package and instructions tailored to the customer's purchase:

The paymentOption object structure is as follows:

For the full API specifications, refer to Klarna Web SDK.

Follow the payment presentation instruction

This section describes how to apply Klarna’s payment presentation instructions, which define how Klarna should appear in your checkout. Following these instructions ensures a consistent experience across payment states and is required for features like Klarna Express Checkout and Sign in with Klarna.

The instruction attribute has the following values:

For the full API specifications, refer to Klarna Web SDK.

Here are example outcomes illustrating how Klarna should be displayed for each instruction:

Show Klarna	Preselect Klarna	Show only Klarna

The presentation instructions are derived from possible customer purchase journeys described in the How to present Klarna article.
Sample code:

function renderKlarna(paymentPresentation) {
  if (!paymentPresentation) return;

  const root = qs("#klarna-payment-method");
  if (!root) {
    console.error("Missing #klarna-payment-method container.");
    return;
  }

  root.innerHTML = `<div id="klarna-option-default" class="klarna-option default" style="display:none;">

</div>

Mount payment option components

Once an instance of PaymentPresentation is created, the Klarna payment option(s) must be rendered dynamically in the payment selector according to Klarna’s presentation guidelines. The following diagram displays different visual components and how they are rendered in different selection states:

1. Icon
2. Badge
3. Header
4. Subheader
5. Message
6. Terms
7. Button

Mount the Klarna payment option components within your designated Klarna payment method container to render them dynamically in the payment form. Ensure that all components—including those not immediately visible—are mounted during initialization, and manage their visibility through your own logic or UI controls.

function renderKlarnaOption(containerId, option) {
  const container = qs(`#${containerId}`);
  if (!container) {
    console.error(`Missing #${containerId} container.`);
    return;
  }

  const ids = {
    icon:    `${containerId}-icon`,
    header:  `${containerId}-header`,
    subhdr:  `${containerId}-subheader`,
    badge:   `${containerId}-badge`,

Handle payment option selection and deselection

When a Klarna payment option is selected/deselected, ensure the additional visual components are shown/hidden properly.

/**
 * Toggle the Klarna payment option selected state.
 * Use for both SDK preselection (PRESELECT_KLARNA) and user interactions.
 */
function toggleKlarnaPaymentOptionSelection(containerId, isSelected) {
  const container = qs(`#${containerId}`);
  if (!container) {
    console.error(`Missing container #${containerId}.`);
    return;
  }

  const display = isSelected ? "block" : "none";

Configure payment button

The payment presentation instance allows you to mount the prebuilt button component. The Klarna Payment Button is context-aware and dynamically adapts to your configuration.

[ Klarna payment button variants]

Choose the theme and shape of the payment button to best fit into your online store in a way that complements your brand and encourages user engagement. More details on the button styling can be found here.

[ Configure Klarna payment button]

The paymentButton.component() can be configured with the following set of parameters:

For the full API specifications, refer to Klarna Web SDK.

Sample code

option
  .paymentButton
  .component({
    id: "klarna-payment-button",  // optional test hook
    shape: "pill",                // "default" | "pill" | "rect"
    theme: "default",             // "default" | "light" | "dark" | "outlined"
    intents: ["PAY"],
    initiationMode: "DEVICE_BEST", // "DEVICE_BEST" | "ON_PAGE" | "REDIRECT"
    initiate: (klarnaNetworkSesionToken, paymentOptionId) => initiateKlarnaPayment(klarnaNetworkSesionToken, paymentOptionId)
  })
  .mount(`#${containerId}-payment-button`);

Starting payment processing involves coordinating the frontend and backend to securely initiate the Klarna Purchase Journey once the customer clicks the Klarna button. This process ensures the customer’s intent is captured, a Payment Request is created, and Klarna Purchase Journey is launched in a seamless and reliable way.

On a high level, the process involves:

1. Capturing the customer’s action when they click the Klarna button.
2. Forward the payment context to the backend.
3. Creating a Payment Request through Klarna’s APIs.
4. Returning the result to the frontend to start the Klarna Purchase Journey.

Retrieve the interoperability_token and payment_option_id (frontend)

async function initiateKlarnaPayment(paymentOptionId) {
  try {
    // 1) Get a klarna network session token from the Klarna SDK
    const klarnaNetworkSessionToken = await klarna.Network.Session.token();

    // 2) Ask your backend to create a payment request
    const response = await fetch('/api/payment-request', {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ klarnaNetworkSessionToken, paymentOptionId })
    });

Create Payment Request (backend)

Call the Payment Request API to initiate a transaction. If customer verification is required, Klarna processes the request and creates a unique payment identifier for tracking. The payment request is then returned in the SUBMITTED state with the interaction details needed to complete the payment flow.

Request

{{#lst:Klarna Docs - Payment Request - Content Source|payment request: create: request: one-time payment}}

Configure customer interaction parameters

The return_url and app_return_url parameters define the redirect targets when the Klarna interaction ends, regardless of whether the purchase is approved or aborted. Correct configuration of these URLs is required to ensure customers return to the correct web or mobile app context and can continue the checkout or post-purchase flow without interruption.

• return_url
  • Used for web-based flows. After the customer completes or aborts the Klarna purchase flow, Klarna redirects the customer to this URL. This may be a URL owned by the Acquiring Partner (which then handles further redirection) or a URL provided by the Partner.

• app_return_url
  • Used for mobile app flows. During the purchase journey, the customer may be redirected to the Klarna app or a third-party app (for example, a bank app). This URL allows Klarna to return the customer to the Partner’s mobile app. The app_return_url must be a registered URL scheme (for example, partnerapp://klarna) or a universal link that resumes the payment flow. The Partner must reopen the integrating app in its previous state, without triggering additional navigation or state changes.

Visual representations for Web flow and App handover flow:

Web handover	App handover

Requirements

• Accept the return URL parameters in the Partner-facing APIs.
• Validation should be implemented, but it must not be more restrictive than what is specified in Klarna’s Payment Authorize API.
• Forward the return URL parameters unmodified to Klarna.

Provide supplementary purchase data

Supplementary Purchase Data refers to additional transaction details shared with Klarna that provide greater context about a purchase. These data points—such as line items, subscription details, or industry-specific attributes—help improve underwriting accuracy, fraud assessment, and the customer’s post-purchase experience. They may be required in certain industries and support multiple use cases, including better acceptance rates, enhanced fraud prevention, improved customer experiences within the Klarna app, and more effective risk monitoring.

Response

Payment Request

POST:/v2/accounts/{partner_account_id}/payment/requests

Response Body

Show recommended

Parameter	Required	Description
state SUBMITTEDIN_PROGRESSCOMPLETEDCANCELEDEXPIREDDECLINEDSUBMITTED	Yes	The current state of the Payment Request. SUBMITTED - The payment request has been submitted to Klarna. IN_PROGRESS - The customer is actively in the payment flow. COMPLETED - The customer has approved the request. In case of o... Show more
payment_request_id	Yes	The unique identifier for the payment request. This is the identifier you will use to reference the payment request in subsequent API calls. You should not make any assumption about the format of this identifier, you should treat it as an... Show more
expires_at	Yes	The expiry time of the payment request. After this timestamp the payment request will be canceled and deleted.
currency	Yes	Currency in ISO 4217 format.
amount	No	Total amount of a one-off purchase, including tax and any available discounts. The value should be in non-negative minor units. Eg: 25 Dollars should be 2500. This is the amount that Klarna will charge the customer for a one-off purchase. S... Show more

Here you can find all required parameters for this operation createPaymentRequest

When the request succeeds, Klarna returns a payment request in the SUBMITTED state.

The response includes:

1. payment_request_id — a unique identifier for the payment request.
2. payment_request_url — the URL used to initiate the customer’s purchase journey.

Sample payload

{
  "payment_request_id": "krn:payment:eu1:request:10be1d49-7beb-6b24-b9dd-8c14d0528503",
  "state": "SUBMITTED",
  "state_context": {
    "customer_interaction": {
      "method": "HANDOVER",
      "payment_request_id": "krn:payment:eu1:request:10be1d49-7beb-6b24-b9dd-8c14d0528503",
      "payment_request_url": "https://pay.klarna.com/l/ZjW2Xipgh0tjbrBGD7hzJM"
    }
  },
  "expires_at": "2025-02-26T17:25:34.534721775Z",
  "created_at": "2025-02-24T17:25:34.534721775Z",

Handle the response (frontend)

Share the payment request ID acquired from the server side as a response to the initiate callback:

async function initiateKlarnaPayment(paymentOptionId) {
  try {
    // 1) Get a klarna network session token from the Klarna SDK
    const klarnaNetworkSessionToken = await klarna.Network.Session.token();

    // 2) Ask your backend to create a payment request
    const response = await fetch('/api/payment-request', {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ klarnaNetworkSessionToken, paymentOptionId })
    });

Configure initiationMode

The initiationModeis a parameter which controls how the Klarna Purchase Journey is launched (redirect / modal window) on different devices (mobile/desktop/native):

After a successful initiation, the Klarna Purchase Flow is presented to the customer, allowing them to:

• Authenticate with Klarna (e.g., via login or one-time passcode)
• Select their preferred payment method (such as Pay in 3, Pay Later, etc.)
• Confirm and complete the payment

To retrieve the required token(s), Klarna provides multiple integration methods. Subscribing to Klarna webhook events is required and may be combined with additional methods to improve resilience.

Using webhooks ensures reliable completion handling, particularly when the customer closes the browser before returning, network interruptions occur during redirects, or post-processing is required before notifying the customer.

The klarna_network_session_token is issued by Klarna after the customer approves the purchase. Use this token to finalize the authorization and create the corresponding Klarna payment transaction.

Method: Subscribe to webhook events (required)

Subscribe to the payment.request.state-change.completed webhook event using the guidelines provided here. Klarna sends this event when the Payment Request reaches the COMPLETED state.

This event indicates that the customer has finished the step-up interaction and that the Acquiring Partner can proceed with finalizing the authorization.

Sample payload

{
  "metadata": {
    "event_type": "payment.request.state-change.completed",
    "event_id": "d9f9b1a0-5b1a-4b0e-9b0a-9e9b1a0d5b1a",
    "event_version": "v2",
    "occurred_at": "2024-01-01T12:00:00Z",
    "correlation_id": "2d1557e8-17c3-466c-924a-bbc3e91c2a02",
    "subject_account_id": "krn:partner:global:account:live:HGBY07TR",
    "recipient_account_id": "krn:partner:global:account:live:LWT2XJSE",
    "product_instance_id": "krn:partner:product:payment:ad71bc48-8a07-4919-[...]",
    "webhook_id": "krn:partner:global:notification:webhook:120e5b7e-abcd-4def-[...]",
    "live": false

Consult the API reference for a complete description of the webhook payload.

Method: Read the payment request

As an alternative method, retrieve the Klarna token(s) by calling the Read Payment Request API.

Once the Payment Request reaches the COMPLETED state, the token(s) are available in the state_context object of the Payment Request.

Sample payload

{
  "payment_request_id": "krn:payment:eu1:request:10be1d49-7beb-6b24-b9dd-8c14d0528503",
  "state": "COMPLETED",
  "previous_state": "IN_PROGRESS",
  "state_context": {
    "klarna_network_session_token":"krn:network:eu1:live:session-token:[...]"
  },
  "expires_at": "2025-02-26T17:25:34.534721775Z",
  "created_at": "2025-02-24T17:25:34.534721775Z",
  "updated_at": "2025-02-24T17:25:34.534721775Z",
  "payment_request_reference": "request-reference-1234",
  "amount": 11836,

Make sure to add the interoperability_token received via the webhook and the purchase details within the call to Worldline. If everything is implemented correctly, Klarna will approve the payment transaction.

curl -X POST https://api.acquiring-partner.com/payment \
  -H "Content-Type: application/json" \
  -d '{
    "amount": 1000,
    "currency": "USD",
    "payment_methods": {
      "klarna": {
        "klarna_interoperability_token": ""
      }
    }
  }'

In rare cases where there's discrepancy between the amount and purchase details submitted in the original payment request and the information submitted to Worldline, Klarna may reject and ask the customer to approve the purchase again.