There are two types of tickets in this game.
1- Green tickets: You can use them to put products that you don't have at that moment at the Airport or Online orders.
How to use them: Tap on any specific order from the Airport or the Online orders and tap on "Use coupon". Like this, you will have it covered in a blink of an eye!
2- Pink tickets: You can use them to search for a specific product that you need at the Merchant, so you will be able to buy it immediately even if he didn't have it in the first place.
How to use them: Tap on the Merchant and then on the Pink ticket and then select the item you are interested in. Then choose one of the three offers he will give you, pay the corresponding price and you have it!