hikashopUpdateVariant not setting the variant!

-- HikaShop version -- : 3.1.1
-- Joomla version -- : 3.7.1
-- PHP version -- : 7.1.2
-- Browser(s) name and version -- : chrome/safari latest on mac
-- Error-message(debug-mod must be tuned on) -- : no error

I have a customised view (which is working fine on a live hikashop 2.x site).

In this view I am automatically setting a variant's value via a Javascript call (depending on where the user is in the site).

Basically, I use the following logic:-

1. I check to see if the page is in the section of the site where I need to set the variant.
2. If it is:-
I get the specific characteristic element (hikashop_product_characteristic_5)

var SetFragrance = document.getElementById("hikashop_product_characteristic_5");

SetFragrance.value = the_characteristic_option_id;

hikashopUpdateVariant(SetFragrance);