To get this achievement you have to find the IAGO invitation in the first floor bathroom (from the entrance with the big staircase go right through the door, then right once again and the first door on the left is the bathroom).
If you are carrying a firearm, use this opportunity to conceal it in the wastebasket.
Leave the bathroom and go outside into the garden. Go left until you see an entrance guarded by two CICADA security guys. Show them the invitation, enter, go right, show the invitation to the guards at the staircase, go up and then left, get frisked (that's why it's important to leave your gun behind), go up and right.
Enter the auction room, sit down and wait for Dalia to greet you. The achievement will unlock.