Use the Boss Musical E-Ticket scanner.

Point your phone's camera at the QR code of the ticket and the Ticket will be validated and checked in!
You also see:
...for which performance/event the ticket is valid
...what the row and seat numbers are
...whether the ticket has already been scanned
...whether the ticket is (in)valid
...how many tickets have been scanned for 'this' performance

Upon first use, you must register your device for access. Once approved, you will be able to use the app immediately.

* Give permission to use the camera at the first boot