I'm trying to purchase the Sleipner Mount, however I checked with my bank, my card is perfectly fine and so is my steam. I tried to make the payment to purchase it, and I'm met with this.

An error has occurred.
Please confirm the status of any relevant options and then try again.
For details, please contact the Square Enix Support Center.
(Error code: 401)

Is anyone else experiencing this? I tried straight through my card, tried buying Crysta (Even that doesn't work) and also tried to do my Steam Wallet.