UNSW

Hi, i'm an international student and I was trying to accept my offer through myUNSW and they asked for my UNSW ID. They said it's located at the top right of the "Offer Letter" that i'm supposed to have. However, i ony have the "Course Offer Summary" and "Offer of Admission" that was sent through UAC and none of them have any kind of ID as they described. Do you have any idea what this "Offer Letter" is? Thanks