WooCommerce Admin-Only Coupon Code

<?php

/**
 * Add a checkbox to the coupon data panel to mark the coupon as "Admin Only".
 */
add_action('woocommerce_coupon_options', 'cwpai_add_coupon_option_field', 10, 2);
function cwpai_add_coupon_option_field($coupon_id, $coupon) {
    woocommerce_wp_checkbox(array(
        'id'          => '_cwpai_admin_only_coupon',
        'label'       => __('Admin Only Coupon?', 'woocommerce'),
        'description' => __('If enabled, this coupon can only be applied manually by an administrator in the backend.', 'woocommerce'),
    ));
}

/**
 * Save the "Admin Only" checkbox value when the coupon is saved.
 */
add_action('woocommerce_coupon_options_save', 'cwpai_save_coupon_option_field', 10, 2);
function cwpai_save_coupon_option_field($post_id, $coupon) {
    update_post_meta($post_id, '_cwpai_admin_only_coupon', isset($_POST['_cwpai_admin_only_coupon']) ? 'yes' : 'no');
}

/**
 * Restrict the usage of the coupon based on the "Admin Only" setting.
 */
add_filter('woocommerce_coupon_is_valid', 'cwpai_restrict_coupon_for_customers', 10, 3);
function cwpai_restrict_coupon_for_customers($valid, $coupon, $discounts) {
    if (get_post_meta($coupon->get_id(), '_cwpai_admin_only_coupon', true) === 'yes') {
        // Check if it's the admin area or if the current user can manage WooCommerce (i.e., an admin).
        if (is_admin() && current_user_can('manage_woocommerce')) {
            return $valid; // Allow admins in the backend.
        } else {
            throw new Exception(__('This coupon is for admin use only.', 'woocommerce'));
            return false;
        }
    }

    return $valid;
}