Open link on new tab when place order is clicked

I have created a custom payment gaeway where user can place order through whatsapp. When place order is clicked I want to open whatsapp url in the new tab and thank you page in same tab. I am stuck at sending the customer to the whatsapp url and at the same time open thank you page in same tab.

Here is the full code of custom payment gateway:

class WC_Gateway_WhatsApp extends WC_Payment_Gateway
{

    public function __construct()
    {
       //... predefined variables

        add_action('woocommerce_update_options_payment_gateways_' . $this->id, array($this, 'process_admin_options'));
    }

    public function init_form_fields()
    {

        $this->form_fields = array(
            //...fields
        );
    }

    public function payment_fields()
    {
        $order_id = absint( get_query_var( 'order-pay' ) );
        $order = wc_get_order( $order_id );

        echo '<p>' . esc_html__($this->description, 'woocommerce') . '</p>';
        ?>
        <script type="text/javascript">
            jQuery(document).ready(function($) {
                const form = $("form.checkout");
                form.submit(function(e) {
                    if (form.find("input[name='payment_method']:checked").val() === "whatsapp") {
                        e.preventDefault();
                        const whatsappUrl = $('#whatsapp-url').data('url');
                        window.open(whatsappUrl, "_blank");
                        form.unbind('submit').submit();
                    }
                });
            });
        </script>
        <?php
    }

    public function process_payment($order_id)
    {
        $order = wc_get_order($order_id);
        $order->set_payment_method($this->id);
        
        $order->save();

        $whatsapp_url = $this->generate_whatsapp_message($order);
        echo '<input type="hidden" id="whatsapp-url" data-url="' . esc_url($whatsapp_url) . '" />';

        return array(
            'result'   => 'success',
            'redirect' => $this->get_return_url($order)
        );
    }

    private function generate_whatsapp_message($order) {
        $customer_name = $order->get_billing_first_name() . ' ' . $order->get_billing_last_name();
$whatsapp_message = "Order from " . $customer_name . ":n";
        $whatsapp_message .= "Order Id = " . $order_id . "n";        
//...other message
        $whatsapp_number = $this->number;

        $whatsapp_url = 'https://wa.me/' . $whatsapp_number . '?text=' . urlencode($whatsapp_message);
        return $whatsapp_url;
    }
}