Assassin's Creed Unity - Stealth Play "Heads Will Roll" Co-op Mission (Solo)

Mission: Heads Will Roll Co-op Mission (Solo)
Didier Paton, a spy working for Robespierre, has gathered information on the Templars, but he was betrayed and sentenced to death. Paton's notebook is in Le Chatelet prison, and Paton's headed to the guillotine - you need to get both.
Armor:
- Legendary Phantom Hood
- Legendary Musketeer Coat
- Legendary Military Bracers
- Legendary Military Belt
- Legendary Phantom Breeches
Weapon: Sword of Eden, Upgraded Gold Plated Pistol

[@Eaglejaw]

Hello bro i have a problem in this mission thats i cant open the chest after i took the key from the officer
The obgagtive didn't update and when i go to the chest nothing happen and i cant open it do u know any solution ?