How to Purchase and download windows version with a discount code

I and trying to purchase and download TurboTax Premier to my computer.  I do not want to start or do my taxes online.  My brokerage company gives me TurboTax for free every year and I was have issues getting the link, so they sent me a discount code to enter when I purchase.  After finally finding the location that I could purchase, when I get to the submit payment, there is nowhere in the process to enter the code for it to discount the cost.  Can anyone help?