Was the item and event-related item or a normal one? It's usually displayed shop on whether it is either. If it was an event item, please check your event board (as event items will only appear there and not on the mainboard).
In addition to that, sometimes items/packages purchased don't display in-game. Many users reported receiving the offer after completely quitting the game and restarting the app. If the offer/item is still missing, please contact us via the support in-game or on discord.