If you received a coupon code for a course, you may enter this on the payment page after selecting Upgrade to Verified or selecting the verified track when enrolling. 

After selecting the Verified track and before checking out, you will see the coupon code entry link below the course image on the payment page.

Select this to open the code field. Once successfully entered you will see the updated price and can select Checkout, or Checkout with PayPal, to complete the transaction.