There is an active discount by promo code for the domain registration service plan. When registering a domain from the customer's control panel using "Register New Domain" link, the promo code is correctly validated (a message
The promotion code "CODE" has been applied successfully appears on clicking "apply"), but the prices are not recalculated according to the discount, the final price does not change.
The issue is confirmed as a bug, #PBA-57100.
The bug is expected to be fixed in the upcoming PBA update. As a workaround the link "Buy more service" can be used, there the discount is validated and applied correctly.