The reason why you cannot log in is because there are more people that are playing than what Square Enix wanted or predicted. They manage server space through projected growth. Anyone who starts playing past that point is an unplanned addition. Normally, profit-seeking companies want as many customers as possible, but at the present time, Square Enix cannot accommodate those new players. Personally, I think the game should be taken down from the store until it can accept new players. It’s dishonest marketing to sell a service to customers when said customers can no longer be accommodated. Until then, I’d advise that new players turn away from the game and not play or buy until Square Enix expands server capacity or the game falls in popularity, both of which may take months.