Having the same problem, sub was supposed to auto-renew overnight but it didn't go through (no reason that it shouldn't have on my side). When I tried to put my card back on file I got hit with the 601 error. So far I've seen a handful of others affected just today so I think it is a square enix side issue. I put in a ticket, will see, but hopefully they've already got people on it and it gets resolved.