There are two ways you can apply a Discount or Promo Code within your Sales & Orders account.
Billing Step: Onboarding Wizards (New Account)
On the Billing Step of any of the Onboarding Wizards for channels and programs in S&O, type in or copy/paste your code in the field provided:
Billing Profile: Shopping Cart (Existing Account)
If you've already passed one or more of the Onboarding wizards in your Sales & Orders account:
Navigate to Billing from the main navigation menu on the left
Locate the Cart flyout menu in the top right corner
Type in or copy/paste your code into the field provided