-- HikaShop version -- : 2.6.0
-- Joomla version -- : 3.4.4
-- PHP version -- : 5.6.13
-- Browser(s) name and version -- : any
I have another post but haven't any resolution to this. I can reproduce the issue on your own demo site.
The problem:
1. A user visits the store, selects a product and proceed to checkout.
2. On the discount code field they enter a valid coupon/discount code. The discount is applied to the shopping cart.
3. If the shopper leaves the checkout page, adds an item to the order or changes a quantity, anything that causes the page to refresh (either by leaving it and coming back again, etc.), the discount is gone and the input box for the discount code is back again.
4. However, now you cannot enter the discount code again. Any attempt to reuse the discount/coupon code does nothing.
You have to clear all cookies from the browser session before the shopping cart is functional again. This is difficult to explain to customers and wasn't an issue in the past. We only noticed it after the update to 2.6.0 but I can not say that the issue wasn't already there in earlier versions.