If you received a coupon code for a course, you may enter this on the payment page after selecting Upgrade to Verified from your edX dashboard or selecting the verified track when enrolling.
To apply the coupon, paste your code into the Add coupon code field and then click the Apply button before placing the order.
After clicking Apply the discount will appear and the total will be reduced. Make sure this reduced total shows before you complete the order with the Place Order button. A message "Coupon code '[your code]' added to basket." will also display at the top of the page.
If you did not add your code before clicking Place Order you may unenroll for a refund, then re-enroll and pay again with the coupon applied.