Your confirmation e-mail is a form of receipt that you can use. You can search your inbox for firstname.lastname@example.org in order to pull these emails up. You can also view your past transactions by navigating to the History tab in your SeatGeek account.
If you cannot locate your confirmation email please feel free to contact us by scrolling down and tapping Contact Support while viewing your order in the SeatGeek app. Click here to see how.