The reply:

Thank you for contacting the North American SQUARE ENIX Support Center. We appreciate you taking the time to contact us for assistance.

We apologize for any inconvenience you have experienced with our authentication systems. The i2501 error is an error that is triggered by the system to protect accounts. Many actions can trigger this error, such as a slow internet connection, use of a VPN or an odd connection (EG: schools or cafes), a possible virus detected on the device, many rapid attempts of payment at once, and numerous other actions. Please check to see if any of the listed actions apply to your situation before attempting to access our services again. We also suggest resetting the connection you are using to connect to the Internet and waiting a full 24 hours since your last attempt before trying again.

Thank you for contacting the SQUARE ENIX Support Center.