Why my unlock code is not working for my Asus Zenfone 2E?

[AC Question]

I made a request to AT&T to unlock my Asus Zenfone 2E as I moved back to France.
I received the unlock code but it is not working!

I tried couple times and it says that there's an error to unlock the network. It's difficult and expensive for me to call AT&T in the U.S.

Please, some help needed!