Trigger a Discount Code from Radio button

-- HikaShop version -- : 5.5.0
-- Joomla version -- : 3.4
-- PHP version -- : 5.6

I want to create a Discount code that will be triggered from a radio button , which will be placed just above the the Discount Code area on checkout page.
How should I write a code for that? Where should i write a code for it?
And how to create a Radio button on check box page?

Hello,

How should I write a code for that? Where should i write a code for it?
And how to create a Radio button on check box page?

In Britain , disabled people can apply for VAT-EXEMPTION so I want a radio button on checkout page such that if I select yes for vat-exemption , VAT amount should not be applied by the customer

In Britain , disabled people can apply for VAT-EXEMPTION so I want a radio button on checkout page such that if user select yes for vat-exemption , VAT amount should not be applied to the customer

I have hika shop free edition , can I do that part in free edition???