Passing discount coupons to Yandex Pay

const paymentData = {
    // ... other parameters
    cart: {
        // ... cart parameters

        // coupons applied by the user
        coupons: [
            { value: '<COUPON_VALUE>' },
        ],
    },
}

function onYaPayLoad() {
    const YaPay = window.YaPay;

    // Payment details
    const paymentData = {
        // For debugging, you need to explicitly specify the `SANDBOX` environment.
        // For the production environment, you can omit this parameter or specify `PRODUCTION`.
        env: YaPay.PaymentEnv.Sandbox,

        // Version 2 points at paying via Yandex Pay
        // The user pays in the Yandex Pay form,
        // and only the result of the payment transfer is returned to the merchant
        version: 3,

        // Code of the currency in which you are going to accept payments
        currencyCode: YaPay.CurrencyCode.Rub,

        // Merchant ID received on registration in Yandex Pay
        merchantId: '<YOUR_MERCHANT_ID>',


        // IMPORTANT!
        // Paid order ID
        // If it's available, the payment form is shown
        //               rather than the checkout form
        orderId: 'order-id',

        // Details of the customer's cart (optional)
        cart: {
            // Items in the cart
            items: [
                {
                    productId: '1',
                    total: '26990.00',
                },
                {
                    productId: '3',
                    // If needed, specify the number of items
                    quantity: { count: 2 },
                    // Total for two items is (7990 * 2)
                    total: '15980.00',
                },
            ],
        },

        // Arbitrary additional data for the cart (optional)
        // After applying encodeURIComponent, the data couldn't be longer than 128 characters
        metadata: 'order-metadata',
    };

    // Payment success handler
    function onPaymentSuccess(event) {
        // Order placed successfully
        // show the order success screen to the user
        console.log(`OrderId — ${event.orderId}\nMetadata — ${event.metadata}`);
    }

    // Payment error handler
    function onPaymentError(event) {
        // Show a message that the payment method is unavailable at the moment
        // and suggest the user to try another method.
        console.log(`Payment error — ${event.reason}`);
    }

    // Payment cancellation handler
    function onPaymentAbort(event) {
        // The user closed the Yandex Pay form.
        // Suggest the user to try another payment method.
    }

    // Create a payment session
    YaPay.createSession(paymentData, {
        onSuccess: onPaymentSuccess,
        onAbort: onPaymentAbort,
        onError: onPaymentError,
    })
        .then(function (paymentSession) {
            // Show the Yandex Pay button on the page.
            paymentSession.mountButton(document.querySelector('#button_container'), {
                type: YaPay.ButtonType.Checkout,
                theme: YaPay.ButtonTheme.Black,
                width: YaPay.ButtonWidth.Auto,
            });
        })
        .catch(function (err) {
            // Couldn't create a payment session.
        });
}