Similar issue. Upgraded from PS3 to PS4 version. PSN store tells me the code has already been used when I click confirm.

Fortunately I was part of Beta 2 on the PS4 so I've got a client, but if this is anything like the other opening stages (PS3/PC) then there's going to be a large number who get exactly this issue but without having the client through other means.

Someone kick this up the line before it becomes a major issue for people please.