Woocommerce cooupon code

Hi

The coupon codes aren’t working:
http://karisma.marketing/product/evaluation-web/

When we clic on apply code bouton (karisma199 or karisma99) we are redirected to an 500 error page displaying:

Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request

What should we do? remove then reinstall Woocommerce (We’re using 2.3.9) ???

Thanks!

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