In Trouble Brewing, if an incorrect order is made, an "X" will appear after you click on the green button to serve the drink.
In the screenshot below the order calls for 1 sugar. However, 2 sugars have been placed in the cup. To correctly fill this order you need to use only 1 sugar.
Therefore, when the green button is clicked to serve the drink, an "X" will appear to indicate the ingredients were wrong.
Once you place 1 sugar into a cup and start the order, the order ticket will disappear. Any order tickets that you see are ones you have not started filling yet.