As you might have noticed, the spending confirmation window does not appear sometimes when you spend Airport Cash. That means you chose "Do not show again". Here’s the list of all situations in which the notification window will be turned off if you make such a choice:
1. Waste of Airport Cash
2. Exclusion of a player from the space program
3. Loss of an item/gift that exceeded 100 in stock
4. Loss of excess fuel in Fuel Station H
5. Removal of all gifts from the list of received gifts
If you want to receive confirmations in the situations mentioned above, do not turn off the confirmation window.