Coupon checkout calculation problem

-- url of the page with the problem -- : shop.conformance.co.uk/
-- HikaShop version -- : 6.3.0
-- Joomla version -- : 5.4.3
-- PHP version -- : 8.2.30

Hi,

I've been presented with a curious problem and wonder if you can help me resolve it.

My checkout is configured to show total prices of product including taxes.

I have discount coupon code of 10% that can be applied at the checkout.

When I apply the code, the system calculates the new overall price and including the removal of the cost of tax, however the checkout page still shows the old tax and not the new tax.

For instance if I have a product that costs £50 with 20% tax the tax is £10 and the total price is £60 - that's fine.

When I apply the code of 10%, the total price reduces by 10% to £54, which is correct including reduction of tax, but the tax line is still saying £10, it should say £9.

Do I need to make a change to the configuration or is this a general problem?

I have attached screenshots to illustrate.

Any advice grately appreciated - as always.

Kind Regards

Duncan