add woo commerce fields

i want to add WooCommerce custom fields edit functions.php
i add this code

add_action('woocommerce_after_order_notes', 'custom_checkout_field');

function custom_checkout_field($checkout) {
    echo '<div id="custom_checkout_field"><h3>' . __('Custom Field') . '</h3>';

    woocommerce_form_field('custom_field_name', array(
        'type'        => 'text',
        'class'       => array('custom-field-class form-row-wide'),
        'label'       => __('Enter Custom Data'),
        'placeholder' => __('Custom placeholder'),
        'required'    => false,
    ), $checkout->get_value('custom_field_name'));

    echo '</div>';
}

but not show in woo coomrece checkout page

any one help plzzz