Upvote:1
From their help:
How do I use digital tickets?
We’ll show you whichever option is available for your route, just search your journey as normal.
Trainline etickets
eticket
Open the email we send you with the PDF(s) attached – this is separate to your booking confirmation email If you like, you can add the eticket(s) to our app or Apple Wallet Scan the QR code from your phone at the ticket gate at the station, or show to staff
Mobile Ticket - you’ll need our app
Open our app and go to My Tickets Tap your Mobile Ticket to activate it just before you travel – once activated, you can’t request a refund Scan the QR code from your phone at the ticket gate at the station, or show to staff