I have had this same problem for over a year now. I have tried using my debit card, credit card, paypal, ultimatePay credit/debit and pre-paid debit card and none have let me through. I have multiple XIV Accounts and I am getting the errors on all of them. Prior to SE dropping UltimatePay I had been using a merchant under UltimatePay's 'Other' tab called MoneyBookers to pay UltimatePay to pay SE for Crysta which I would then use on my accounts (ridiculous right?).

According to SE; error codes 401/601 is your financial institution rejecting the charge and they state they cannot do anything about it. However, I have had my financial institution do a follow up investigation and they concluded that the charges never even got to them to reject so nothing was rejected on their end. I then turned to SE support with all of this information and while I was explaining my issue they simply spammed their copy/paste response to me

You: I have tried Credit, Debit, UltimatePay, Paypal
Agent Daniel W: Understood. Well let me see if there is any advice we can give you. I need to verify an account. Please give me an ID.
You: and I make sure to only try once every 24 hours
You: all of those resulted in a 401 error
Agent Daniel W: Understood. Well let me see if there is any advice we can give you. I need to verify an account. Please give me an ID.
You: However, maybe once every 20 days or so it will work, which only further adds to my confusion
Agent Daniel W: Understood. Well let me see if there is any advice we can give you. I need to verify an account. Please give me an ID.

Clearly they were not even reading the case I was making. The support person then went on a tangent claiming they could not look up my account info due to XI maintenance.. I have not been subbed to XI since 2010. At this point I felt like the guy was just trying to close the ticket so he could go on break or something but I insisted he look at another of my accounts which has never been used for XI. He then followed up with a 'nothing I can do' response and told me to buy a game time card.

While a game time card could be a solution; if you have a legacy account you are paying an extra $5/mo. This also is of no use if you would ever like to use the cash shop! I hope someone does read this as it is a huge issue that is preventing financially capable players from playing and causing SE to lose revenue.