Once the customer has selected Klarna and decided to proceed to the payment with Klarna, Acquiring Partners are expected to authorize the payment with Klarna and allow the customer to go through Klarna's Purchase Journey.

The following sequence applies:

1. Customer clicks on the Klarna Payment button
2. The javascript function attached to the button click handler initiate is triggered
3. Acquiring Partner’s backend call Klarna’s Payment Authorize API
4. Klarna returns one of the following responses:
   1. APPROVED – transaction is completed.
   2. STEP_UP_REQUIRED – customer needs to go through Klarna's Purchase Journey
   3. DECLINED – payment was denied.
5. The javascript function attached to the initiate button click handler returns a promise resolving to the authorization result

As described in the previous section, once the customer has selected the Klarna payment option in the payment selector, the Acquiring Partner will need to render the Klarna Payment Button.

The Acquiring Partner will need to configure paymentButton component from the paymentPresentation instance with the following attributes:

• initiate button click handler: attach a function which triggers your backend to call Klarna’s Payment Authorize API and return a promise resolving to the authorization result.
• initiationMode: This parameter controls how the Klarna Purchase Journey is launched (redirect / pop up window) on different devices (mobile/desktop/native)

Sample code

async function initiateKlarnaPayment(klarnaNetworkSesionToken, paymentOptionId) {
  try {
    // 1) Ask your backend to authorize the payment
    const response = await fetch('/api/authorize-payment', {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ klarnaNetworkSesionToken, paymentOptionId })
    });

    if (!response.ok) throw new Error('Network or server error');
    
    // 2) Handle backend response

The initiate button click handler attribute from the SDK requires the Acquiring Partner to call Klarna's Payment Authorize API and return the results as a promise to the client-side.

• When Partners optimize their integration with Klarna, they are likely to have Klarna Network data points to share with the Acquiring Partner.
• The Acquiring Partner’s Checkout session API should accept klarna_network_session_token and klarna_network_data  parameters and if provided they must be forwarded when calling Klarna's Payment Authorize API.

The Payment Authorize API is used to authorize payments on Klarna Network — whether they are one-time purchases, tokenized payments, token charges, or a final authorization following a step-up flow. All requests must include the applicable supplementary_purchase_data as defined by Klarna Network Rules.

A one-time payment represents the most common scenario, where the customer completes a single purchase with Klarna. The call may return an immediate authorization (APPROVED) or require additional customer interaction (STEP_UP_REQUIRED).

In the request to the Payment Authorize API, specify the following parameters:<br />

Payment Authorize

Copied

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

Path ParametersRequest HeadersRequest Body

Show recommended

Parameter	Required	Description
Copied partner_account_id	Yes	Unique account identifier assigned by Klarna to the onboarded merchant

Here you can find all required parameters for this operation authorizePayment

curl https://api-global.test.klarna.com/v2/accounts/{partner_account_id}/payment/authorize \
  -H 'Authorization: Basic <API key>' \
  -H 'Content-Type: application/json' \
  -H 'Klarna-Network-Session-Token: eyJhbGciOiJIU...' \
  -d '{
        "currency": "USD",
        "supplementary_purchase_data": { .. },
        "klarna_network_data": "<serialized-json>",
        "request_payment_transaction": {
          "amount": 11800,
          "payment_option_id": "***",
          "payment_transaction_reference": "acquiring-partner-transaction-reference-1234"

The response schema is as follows:

When performing a one-time payment or token charge through the Payment Authorize API, Klarna returns a response that reflects the result of the payment authorization. Because this flow only includes a request_payment_transaction in the request, the response will always contain a corresponding payment_transaction_response object. The result field inside this object indicates the outcome of the authorization and determines the next step to perform.

The result has the following possible values:

Result: STEP_UP_REQUIRED

When Klarna cannot immediately create a Payment Transaction and a step_up_config was provided in the request, Klarna returns STEP_UP_REQUIRED with a payment_request. The partner must redirect the customer to Klarna’s purchase journey URL to complete authentication and payment option selection.<br>

<br>
When the payment cannot be completed instantly, Klarna returns the payment_request details including the payment_request_id and payment_request_url which should be used to launch the Klarna Purchase Journey.<br>

Sample payload

{
  "payment_transaction_response": {
    "result": "STEP_UP_REQUIRED"
  },
  "payment_request": {
    "payment_request_id": "krn:payment:eu1:request:552603c0-fe8b-4ab1-aacb-41d55fafbdb4",
    "payment_request_reference": "acquiring-partner-request-reference-1234",
    "amount": 11800,
    "currency": "USD",
    "state": "SUBMITTED",
    "expires_at": "2025-01-02T13:00:00Z",
    "created_at": "2025-01-01T12:00:00Z",

Result: APPROVED

When the payment authorization is approved, Klarna returns an APPROVED result and a newly created payment_transaction.<br>
The Acquiring Partner must store the payment_transaction_id for post-purchase operations (capture, refund, etc.) through the Payment Transactions API.<br>

<br>

An APPROVED result means the payment has been authorized successfully without requiring further customer interaction.<br>

Sample payload

{
  "payment_transaction_response": {
    "result": "APPROVED",
    "payment_transaction": {
      "payment_transaction_id": "krn:payment:eu1:transaction:6debe89e-98c0-[...]",
      "payment_transaction_reference": "transaction-reference-1234",
      "amount": 11800,
      "currency": "USD",
      "payment_funding": {
        "type": "INVOICE",
        "details": { }
      },

Result: DECLINED

If Klarna cannot approve the payment, the API returns a DECLINED result without a payment_transaction. Partners should treat this as a final rejection unless instructed by Klarna to retry.

Sample payload

{
  "payment_transaction_response": {
    "result": "DECLINED",
    "result_reason": "PAYMENT_DECLINED"
  }
}

Extract and forward the Payment Authorize API response parameters to your frontend:

• result: the result of the payment authorization attempt
• payment_request_id: The unique Klarna identifier for the payment request

Update the implementation of the initiate callback to support different results:

async function initiateKlarnaPayment(klarnaNetworkSesionToken, paymentOptionId) {
  try {
    // 1) Ask your backend to authorize the payment
    const response = await fetch('/api/authorize-payment', {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ klarnaNetworkSesionToken, paymentOptionId })
    });

    if (!response.ok) throw new Error('Network or server error');

    // 3) Handle backend response