Square Enix Member Code?

[HEC]

You should be able to add / register it here:

https://membership.square-enix.com/users/sign_in

This is basically SE "social" site - the registration is pretty much just to show off your games plus to receive some occasional minor promotions. It will not impact / limit you in any way in regards of gameplay or bonus items received if you don't register the code.

It will after loging in end up at this page when you can register the game:
(Just click on My profile button after login to above page)

http://na.square-enix.com/us/account/ *

Despite having "NA" in url it actually serves my EU account ... SE seems to have a lot of mixed up links between EU / NA.

Edit:

Alternative EU / UK links is:

http://eu.square-enix.com/en/uk/account/ *

Note:

* Each link have 7 digit SE member account number (different for each member indeed)