I searched both the MogStation and the FFXIV Online Store, on both my accounts, and found nothing that would let me even attempt to pre-order Dawntrail. When I checked "Expansions" the sites said there were none available for my accounts.
Edit: I'm a Windows PC subscriber in the US.
Edit2: I've tried using both Firefox and Edge.
Anyone else encountering this issue? Or am I just blind?
