Discount codes are now a feature that org admins are able to manage themselves.
To add discount codes to a current ticketed campaign, click the '...' and then 'edit' next to the campaign.
Then click on the 'discounts' step and then 'enable discount codes'.
Click the 'add a new discount code' button where you'll be presented some fields to complete.
When creating a new campaign that you wish to add discount codes to, you'll progress through to the discounts section when setting up the campaign