Trying to buy the "Heavensward" expansion through the Square-Enix store and im getting this error when i click the checkout button..

INFORMATION
We are unable to process your request at this time. The customer support has already been informed about this situation and will get in touch with you if necessary. (Error ID: 5003)

This is kinda annoying me since i have no idea why i cant buy it. ive been trying on and off during the week to see if it was fixed and it hasnt been. If anyone has any idea as to why this is the case i would be very appreciative.