functions.php

<?php
// Car rental plugin - booking form

add_action('woocommerce_new_order', 'wpgens_save_source_tracker_meta', 10, 1);

function save_source_tracker_meta($order_id)
{
    if (!isset($_COOKIE['_wpgens_st_data'])) {
        return;
    }

    $data = json_decode(sanitize_text_field(stripslashes($_COOKIE['_wpgens_st_data'])), true);

    $data_to_save = [
        "utm_id",
        "utm_source",
        "utm_medium",
        "utm_campaign",
        "utm_term",
        "utm_content",
        "gclid",
        "fbclid",
        "msclkid",
        "visit_date",
        "landing_page"
    ];
    $data_to_save = get_option('wpgens_st_tracking_params', $data_to_save);

    $order = wc_get_order($order_id);
    $order->update_meta_data('_wpgens_st_data', $data);

    foreach ($data_to_save as $key) {
        if (isset($data[$key]) && $data[$key] !== '') {
            $order->update_meta_data('_wpgens_st_' . $key, $data[$key]);
        }
    }

    $order->save();
}