Usually that error occurs when your subscription has lapsed - if you started not that long ago you would have been on a free trial period, which only lasts for about 30 days if I remember rightly. To continue playing after that, you need to add a payment method (credit card, debit card, prepaid time card or another option) to your account, as FFXIV requires subscription fees to be paid in order to play. There is no way around this I'm afraid.

You can add a payment method for your account here on the Mogstation: https://secure.square-enix.com/accou...est=mogstation (after logging in select 'Square Enix Account Settings', and 'Register/Update Payment Method'. Hopefully this has helped.