well it worked for me at least.

i have upgraded my PS4 FF xiv to SB and that was the reason why i could not name change, the error is related in some aspect only to SB expansion , IF , you can access your account via PC or any other way in a previous expansion ( ARR or Heavensward ) you'll be able to see your character model on the log in screen and rename it

at least it worked for me my PC version was on ARR and i was able to rename the char on pc , log out, and now i'm playing on PS4 normally. hope this help you guys too! GL!