Add a custom fee

Hello.

I add optional additional service on checkout by this code:

////////////////   Add a custom checkbox fields after billing fields
add_action( 'woocommerce_after_checkout_billing_form', 'add_custom_checkout_checkbox', 20 );
function add_custom_checkout_checkbox(){

    // Add a custom checkbox field
    woocommerce_form_field( 'klient_gift', array(
        'type'  => 'checkbox',
        'label' => __(' ?My Custom service? </br><span style="font-weight:100;font-size:11px;">description!</span></br>'),
        'class' => array( 'form-row-wide' ),
    ), '' );
}

// Remove "(optional)" label on "Installement checkbox" field
add_filter( 'woocommerce_form_field' , 'remove_order_comments_optional_fields_label', 10, 4 );
function remove_order_comments_optional_fields_label( $field, $key, $args, $value ) {
    // Only on checkout page for Order notes field
    if( 'klient_gift' === $key && is_checkout() ) {
        $optional = '&nbsp;<span class="optional">(' . esc_html__( 'optional', 'woocommerce' ) . ')</span>';
        $field = str_replace( $optional, '', $field );
    }
    return $field;
}

// jQuery - Ajax script
add_action( 'wp_footer', 'checkout_fee_script' );
function checkout_fee_script() {
    // Only on Checkout
    if( is_checkout() && ! is_wc_endpoint_url() ) :

    if( WC()->session->__isset('enable_fee') )
        WC()->session->__unset('enable_fee')
    ?>
    <script type="text/javascript">
    jQuery( function($){
        if (typeof wc_checkout_params === 'undefined') 
            return false;

        $('form.checkout').on('change', 'input[name=klient_gift]', function(e){
            var fee = $(this).prop('checked') === true ? '1' : '';

            $.ajax({
                type: 'POST',
                url: wc_checkout_params.ajax_url,
                data: {
                    'action': 'enable_fee',
                    'enable_fee': fee,
                },
                success: function (result) {
                    $('body').trigger('update_checkout');
                },
            });
        });
    });
    </script>
    <?php
    endif;
}

// Get Ajax request and saving to WC session
add_action( 'wp_ajax_enable_fee', 'get_enable_fee' );
add_action( 'wp_ajax_nopriv_enable_fee', 'get_enable_fee' );
function get_enable_fee() {
    if ( isset($_POST['enable_fee']) ) {
        WC()->session->set('enable_fee', ($_POST['enable_fee'] ? true : false) );
    }
    die();
}

// Add a custom   7hrn fee
add_action( 'woocommerce_cart_calculate_fees', 'custom_percetage_fee', 20, 1 );
function custom_percetage_fee( $cart ) {
    // Only on checkout
    if ( ( is_admin() && ! defined( 'DOING_AJAX' ) ) || ! is_checkout() )
        return;

    $fix_price = 7;

    if( WC()->session->get('enable_fee') )
        $cart->add_fee( __( 'Подарок клиенту', 'woocommerce')." ($fix_price Грн)", ($fix_price) );
		
}

All works fine….

1) But in order some time exist – https://i.imgur.com/06wICQU.png
2) In case when I add discount to role:

add_action( 'woocommerce_cart_calculate_fees', 'discount_based_on_user_role_and_payment', 20, 1 );
function discount_based_on_user_role_and_payment( $cart ) {
    if ( is_admin() && ! defined( 'DOING_AJAX' ) )
        return; // Exit

    // Only on checkout page for 'vendor' user role
    if ( ! ( is_checkout() && current_user_can('vendor') ) )
        return; // Exit

    
    $percentage = 5;

    
        // Calculation
        $discount = $cart->get_subtotal() * $percentage / 100;
        // Applying discount
        $cart->add_fee( sprintf( __("Discount vendor (%s)", "woocommerce"), $percentage . '%'), -$discount, true );
    
}

‘fee’ row additional service not exist – https://i.imgur.com/xlUxl7f.png