(At risk of stating the obvious), you need to pay coins for a floor decoration, not just take it out of your inventory and plop it on the ground. Also try force-restarting the game by closing the app and reopening it. Then it should recognise when you buy a floor decoration. If this still doesn?t work, you?ll need to send a bug report to Storm8. For reference I used the French Lantern but at $45000 it ain?t cheap.