TrenItalia Tickets shows "Not valid for travel"

If you have booked a ticket for an Italian regional train, you will see ‘NOT VALID FOR TRAVEL’ on the booking confirmation:

This means you need to validate your ticket in TrenItalia's app on your smartphone or tablet. You can find it on the Google Play Store (Android) or App Store (iOS). You can find the app using the logo below:

Once you have installed this app, you can put your ticket in this app. Opening the app will take you to the homepage below. You don't need to register by TrenItalia. Go to ‘My Journeys’ => ‘RETRIEVE ANOTHER TICKET’ => ‘Search with PNR /Title Code and Email’ => enter the PNR (Ticket Code) along with your email address with which you used during booking this ticket. The ticket code can be found at the top left of the booking confirmation