My account is an NA account, though I think it is registered as a Steam account (though I don't play it through steam).

I have not "redeemed" my code through that site. The code format it's expecting is XXXXXX-000-XXXXXX-000. I have no such code anywhere in my confirmation email from green man gaming like that. The code I have, marked in the email as "FFXIV Heavensward Early Access:" is a 20 digit code in 5 segments: XXXX-XXXX-XXXX-XXXX-XXXX. It matches what I see in the mog station, though the mog station will not accept it.