Pre-Ordered NHL 25 for Xbox

Hi, I am not sure if I am in the right place or not but I am hoping that someone could help me or direct me to the right place.  I pre-ordered NHL 25 for my son for Xbox and we picked the game up today.  On the bottom of my receipt the sales person told us that there was a special code because we pre-ordered.  I went under his xbox to redeem the code and the code isn't working- just says to try again later.  I am not tech savy and I am not sure if I am doing it right so if anyone could provide me with any guidance or some things to try to get the code to work it would be greatly appreciated.  Thanks.