In order to make a purchase in Thug Life on iOS, the Thug Life iOS application is required. To install the iOS application, please find it on the iOS app store here.
Facebook do not make the option to purchase available through messenger.com versions of games. To make a purchase you must access the game through Facebook.com or the Facebook app instead. If you are entering the game through a Messenger notification, then you will be unable to make a purchase until you launch the game from the Facebook app or via the mobile web version of the game.
You can access the Facebook.com version of Thug Life directly at the following link, which should give you the option to make a purchase: https://fb.gg/play/thuglife-game