If you want to close a ticket, go to the ticket in the activity panel. If you see the ticket click on the orange eye and go to the next step.
Make sure you have selected the right ticket before you end it.
To close the ticket you need to click on the Finish button at the right corner.
You will be redirected to the pop-up window as below. At Results you can choose between: no results, success or failure.
Don't forget to press Save after completing the pop-up.
As you can see, the ticket is closed/finished in the activity panel.