Please fix the freaking website for payments!

[Enkidoh]

Because there actually isn't one particular cause for that error - error codes in general usually are just a way of saying "something has gone wrong here" in the most generic way possible, with the actual underlying cause being far more complex that most realize.

Usually the 401 and 601 errors most commonly are caused by either your bank or card vendor (such as Mastercard or Visa) blocking the transaction on their end because their security department believes it possibly fraudulent (online games are a common target for purchases made on stolen card details), or, the browser you're using to access the Mogstation is blocking a security script from running while you enter the card details (such as Firefox with the Adblock and Noscript addons) - this is what 'Global Collect' is, it's a security system that checks your card details as legitimate, so if it's blocked, naturally nothing works. But there are other causes too which are too complex and numerous to list here. So it mostly becomes a process of elimination of causes to fix the problem.

The first I can suggest is to, a) ring your card vendor (that is, the card company like Visa listed on your card, not the bank who issued you it - the only time I had a payment issue with my debit card was ultimately fixed when I rung Visa about it and it turns out they were the ones blocking the transaction and not the bank at all). If that doesn't work, try a different browser to access the Mogstation (or turn off security functions like script blockers). Otherwise, you might have to contact SE's support line I'm sorry to say.