problem with create a gift certificate

-- HikaShop version -- : 2.6.0
-- HikaSerial version -- : 1.10.1
-- Joomla version -- : 3.4.8
-- PHP version -- : 5.5.12

Hi! i read carefully documentation and many posts on the forum. I do not understand the basic functioning of hikaserial concerning creation of gift certificate.
i wanna create a gift card. An user must buy it to gift at another user: i try, the first user buy a product that is a gift certificate, on the order there is a serial number, another user use this serial on the field coupon before proceed to buy, but i've the error coupon isn't valid.
i do the follow step:
1. i create generator with coupongen plugin
2. i create a pack having 'pack generator' = the value create in step1, and in 'product' i add a product having his price.

Now happens that a user can buy the product 'gift card', the order is created, in the email order there is a serial on its foot.
On hikaserial, serial, i see a new serial create with 'used' status.
if an other user try to use this serial on 'coupon' field during a purchase an error says that the coupon is invald.

Certainly i not do some config step or i don't understand the hikashop functioning .
I attach the screenshot of coupongen, of pack and product
With regards
Roberto

UPDATE: i create a coupon on hikashop as template to link it on coupongen, but issue remain.

HI! tnx for your help...here i attach a screenshot of the configuration of coupongen plugin and of the coupon template.
tnx too for the suggestion about javascript error: i will correct it thanks the link.

Regards
Roberto

Jerome! i dont know how, but i wrong something yesterday.
Adding a coupon template and link it to at coupongen the system works correctly
Sorry for my oversight
i've another some question about hikaserial and his application, but i will open another post.

Thanks a lot

with regards
Roberto