Broadsowrd Online Games have announced that Ultima Online promotional code redemption will be disabled for the rest of the month:

Today (5/26/2016) at approximately 5 pm EDT we will taking down the Promotional Code Redemption Warehouse in preparation of setting up the Ultima Online In-Game store. The warehouse will be down until May 31st when we publish Pub 93 to all shards.

Thank you for your patience and understanding.

The in-game store (not endgame store!) is a fairly significant addition to Ultima Online, so it’s understandable why Broadsword might need to disable other marketplace systems associated with the game ahead of it going live. Presumably, promotional codes not yet redeemed will still be valid after May 31st; certainly, there has been no word to the contrary.