Hi,
You said initially that you have HikaShop 5.0.1. Maybe updating HikaShop to the latest version would help since I don't have the issue with it ? If this doesn't help, then I don't know what the problem is. If it's a security component on your website or your server which is blocking this, then you need to ct on this security component.
A simpler approach would be to not use this setting. If you leave it empty, HikaShop will display instead the default empty cart message in the cart module when the cart is empty. And in that case, you can use a translation override on the CART_EMPTY translation key to set your HTML.