Starting Thursday, January 7th, Founder’s Pack codes cannot be added via your Account Management page. This is by design so don’t worry! If you purchased a Disciple or Master Pack, your account is all set to access the Name Reservation. You do not need to add your code in order to participate in the Name Reservation (begins January 11, 2016 at 6pm PST for NA servers, and 7pm CET for EU servers).
However, you will need to add your Founder’s Pack code once Head Start begins to receive your items! You will be able to add your code via your Account Management page any time after Head Start (begins January 15 at 10am PST / 7pm CET for both NA and EU servers).