404 Error msg after applying coupon code

Hi, when I apply a coupon code I got a page with 404 error. Then when I reload the cart page everything is fine with the coupon applied.

What can I do?

Thanks in advance,

Matteo

P.S. http://thereunion.it/shop/, “SC25TR” coupon for orders of €40 or more.

https://ww.wp.xz.cn/plugins/woocommerce/

### WordPress Environment ###

Home URL: http://thereunion.it
Site URL: http://thereunion.it
WC Version: 2.5.5
Log Directory Writable: ✔
WP Version: 4.5.2
WP Multisite: –
WP Memory Limit: 256 MB
WP Debug Mode: –
Language: it_IT

### Server Environment ###

Server Info: Apache
PHP Version: 5.6.22
PHP Post Max Size: 128 MB
PHP Time Limit: 120
PHP Max Input Vars: 3000
SUHOSIN Installed: –
MySQL Version: 5.6.28
Max Upload Size: 128 MB
Default Timezone is UTC: ✔
fsockopen/cURL: ✔
SoapClient: ✔
DOMDocument: ✔
GZip: ✔
Multibyte String: ✔
POST remoto: ✔
GET remoto: ✔

### Database ###

WC Database Version: 2.5.5
:
woocommerce_sessions: ✔
woocommerce_api_keys: ✔
woocommerce_attribute_taxonomies: ✔
woocommerce_termmeta: ✔
woocommerce_downloadable_product_permissions: ✔
woocommerce_order_items: ✔
woocommerce_order_itemmeta: ✔
woocommerce_tax_rates: ✔
woocommerce_tax_rate_locations: ✔

### Active Plugins (20) ###

LayerSlider WP: by Kreatura Media – 5.6.2
Ultimate Addons for Visual Composer: by Brainstorm Force – 3.16.3
Akismet: by Automattic – 3.1.11
Contact Form 7: by Takayuki Miyoshi – 4.4.2
Essential Grid: by ThemePunch – 2.0.9.1
Go Pricing - WordPress Responsive Pricing Tables: by Granth – 3.1.2
Iubenda Cookie Solution: by iubenda – 1.11.1
Jetpack by WordPress.com: by Automattic – 4.0.3
WPBakery Visual Composer: by Michael M - WPBakery.com – 4.11.2
KingSumo Giveaways: by KingSumo – 1.4.0
LeadPages connector: by LeadPages – 1.2.0.3
Ninja Forms - PayPal Express: by The WP Ninjas – 1.0.10
Ninja Forms - Layout & Styles: by The WP Ninjas – 1.2.7
Ninja Forms - File Uploads: by The WP Ninjas – 1.4.9
Ninja Forms: by The WP Ninjas – 2.9.47
Slider Revolution: by ThemePunch – 5.2.5.3
Under Construction: by Noah Kagan – 1.17
WooCommerce: by WooThemes – 2.5.5
YITH WooCommerce Compare: by YITHEMES – 2.0.8
YITH WooCommerce Wishlist: by YITHEMES – 2.0.15

### Settings ###

Force SSL: –
Currency: EUR (€)
Currency Position: left
Thousand Separator: .
Decimal Separator: ,
Number of Decimals: 2

### API ###

API Enabled: ✔
API Version: 3.1.0

### WC Pages ###

Shop Base: #563 - /shop/
Carrello: #564 - /carrello/
Cassa: #565 - /cassa/
Il mio account: #566 - /il-mio-account/

### Taxonomies ###

Product Types: external (external)
grouped (grouped)
simple (simple)
variable (variable)

### Theme ###

Name: Aktina Child
Version: – 0 è disponibile
Author URL:
Child Theme: ✔
Parent Theme Name: Aktina
Parent Theme Version: 1.6.5
Parent Theme Author URL: http://khothemes.com/
WooCommerce Support: ✔

### Templates ###

Overrides: Aktina/woocommerce/cart/cart-shipping.php
Aktina/woocommerce/cart/cart-totals.php
Aktina/woocommerce/cart/cart.php
Aktina/woocommerce/cart/mini-cart.php
Aktina/woocommerce/content-product.php
Aktina/woocommerce/content-product_cat.php
Aktina/woocommerce/content-single-product.php
Aktina/woocommerce/global/form-login.php
Aktina/woocommerce/global/quantity-input.php
Aktina/woocommerce/loop/loop-start.php
Aktina/woocommerce/loop/orderby.php
Aktina/woocommerce/loop/result-count.php
Aktina/woocommerce/loop/sale-flash.php
Aktina/woocommerce/myaccount/form-edit-address.php
Aktina/woocommerce/myaccount/form-login.php
Aktina/woocommerce/myaccount/form-lost-password.php
Aktina/woocommerce/single-product/add-to-cart/external.php
Aktina/woocommerce/single-product/add-to-cart/grouped.php
Aktina/woocommerce/single-product/add-to-cart/simple.php
Aktina/woocommerce/single-product/product-image.php
Aktina/woocommerce/single-product/product-thumbnails.php
Aktina/woocommerce/single-product/related.php
Aktina/woocommerce/single-product/sale-flash.php
Aktina/woocommerce/single-product/tabs/additional-information.php
Aktina/woocommerce/single-product/tabs/description.php
Aktina/woocommerce/single-product-reviews.php