Do you ever come across fake Etickets that people have made on their phone/computer?
People apparently modify valid tickets and change the text/date and then hope to just show to gateline staff and be waved through. If scanned, their evil plans are thwarted - but a trick is to purposely show an invalid code so it won't work, and hope to be let out by staff assuming a fault with their equipment
I believe in those cases, it's treated as if no ticket was held so won't work. Likewise, I've heard people using apps to simulate that the screen is cracked, and then say 'I can't scan - my phone is broken'. I assume the same happens for them.
Clearly these tickets have already attracted plenty of scams, and TikTok can be thanked for a lot of 'hacks' on how to avoid paying to travel on public transport (including how to open gatelines etc) which is probably why it's becoming a thing. Sadly, such scams are going to be as obvious as people who try all the same excuses for paper tickets and not work out well for the passenger.