When you get a disguise for an restricted area, you get three attempts to stay in cover. The timer reaches the end and a guard will approach you.
You then have a speech challenge.
You can Intimidate, persuade or lie for the trophy.
You must not reset your tries otherwise you resey the trophy progress.
You must perform a speech challenge on a different guard each time, you can't fool the same one over and over.
HelixNubula has pointed out that it worked on the same guard three times on the Groundbreaker. So, where I did it might be a glitch. For the sake of the trophy description, I got this trophy on Monarch.