plugin not creating sub order in my custom function

I am creating order in my custom function, but your plugin not creating sub order. I tried to add

if (function_exists(‘dokan_create_sub_order’)) {
// Trigger Dokan’s sub-order creation function
dokan_create_sub_order($parent_order);
}

but not going in if condition. my crate order function is below:

// Save sales agent Enquiry
function save_order_data() {
global $wpdb;

// Retrieve form data
$product_idsArr = $_POST['product'];
 $variations_idsArr = $_POST['variation'];
$productvalidation=1;
if(!empty($product_idsArr)){
    foreach($product_idsArr as $productId){
        if($productId==""){
                $productvalidation=0;
        }
    }
}else{
    $productvalidation=0;
}

$variationvalidation=1;
if(!empty($variations_idsArr)){
    foreach($variations_idsArr as $variationId){
        if($variationId==""){
                $variationvalidation=0;
        }
    }
}else{
    $variationvalidation=0;
}

$userId = $_POST['users'];
$uservalidation=1;
if($userId==""){
     $uservalidation=0;
}
if($uservalidation==1 && $productvalidation==1 && $variationvalidation==1){

    $order = wc_create_order();
    $order->set_customer_id($userId);
    foreach ($variations_idsArr as $product_id) {
        $product = wc_get_product($product_id);
        $order->add_product($product, 1);
    }
    $order_total = $_POST["grossamount"];
    $order->set_total($order_total);
    $order->save();
    $order_id = $order_id = $order->get_id();
    $sales_agent_id = get_current_user_id();
    $current_user = wp_get_current_user();
    $sales_agent_name = $current_user->display_name;
    $providing_book = isset($_POST["providebook"]) ? 'yes' : 'no';
    if($providing_book=="yes"){
        $booksArr=$_POST["books"];
        $booksCodes=implode(",",$booksArr);
    }else{
        $booksCodes="";
    }
    //update_post_meta($order_id, 'has_sub_order', '1');
    update_post_meta($order_id, 'sales_agent_id', $sales_agent_id);
    update_post_meta($order_id, 'sales_agent_name', $sales_agent_name);
    update_post_meta($order_id, 'providing_book', $providing_book);
    update_post_meta($order_id, 'book_codes', $booksCodes);



    $response = array(
        'success' => true,
        'message' => $order_id
    );

}else{

        $response = array(
            'success' => false,
            'message' => 'Please select user, product and variations.'
        );


}

// Return the JSON response
wp_send_json($response);

}
add_action(‘wp_ajax_save_order_data’, ‘save_order_data’);
add_action(‘wp_ajax_nopriv_save_order_data’, ‘save_order_data’);

How to work yourplugin in my function. Please help.