Can I include a discount code in a URL?
Yes you can. Here's an example: http://example.com/page/?discount=CODE
The important part is the ?discount=CODE where CODE is your discount code.
This code works on any URL on your site, and it's then stored so that it does NOT need to remain in the URL to be used at checkout.
Note: If using this in conjunction with a custom add to cart link, use the & symbol in place of the question mark if the discount code is the last item. Example: http://yoursite.com/?edd_action=add_to_cart&download_id=XXXX&discount=XXXX
Here's an example of a Discount Code in the admin area: