Ì have a US account. I live now in the EU. I use a EU version of the game. I had no issues when I bought the Abyssea content digitally. The SoA expansion installed successfully. I cannot register the expanion on my account page. I get the following message;

You cannot add expanded services because either the maximum number of service accounts have been added/registered or there are no service accounts to which the expanded services can be added/registered.
I was prompted to buy the expansion from SE, to their online store so I did so.