Hi,
Well, if the VAT rate is 0 in the cart, it's normal that the order_discount_tax value is also 0 when the order is created from the cart.
And thus, the problem has nothing to do with HikaShop not properly filling the order_discount_tax value when the order is created from the cart. The problem is that the tax is not calculated for the coupon.
And based on what you wrote, the issue is likely that your taxes are not configured properly for what you want to do.
I've checked your settings with the backend access you provided. I think the issue is with the "apply coupon" setting of the HikaShop configuration:
www.hikashop.com/support/documentation/5...nfig.html#main_taxes
Since that setting is set to "after taxes", it means that the taxes are calculated for the cart, and then the coupon applies to the cart.
You probably want to change that setting to "before taxes". And you also want to change the flat amount of your coupon as you want to provide the value without taxes: 8.13
I've made the changes for you and now the taxes properly updates based on the value of the coupon when added to the cart:
i.imgur.com/a3YiI0R.png