I am having the same problem on my PS5. I can play as the Paladin class in the game, but it will not let me purchase cosmetics for the Paladin class saying that I need to purchase the expansion first… which I did. I also can’t use the mount, pet, and Paladin armor set with deluxe edition… I also keep getting the same error code you are. I keep looking into what’s causing this issue, but haven’t found a work around yet. I’ve tried restoring my license on the game, restarting my PS5, starting a new character, and nothing is working. Hopefully Blizzard fixes this crap soon. If I find anything out, I will post it on here.