They bought a ticket on the app, but were still fined. “Protection period against abuse”, Prague explains
If you buy a ticket in Prague via the PID Lítačka app and go straight to the metro, tram or bus, you risk a fine. People with a paid ticket have to wait two minutes before it officially starts to be valid. Some people have already been fined hundreds of crowns because they couldn’t show their ticket for a few seconds. Representatives of Prague Integrated Transport argue that this is a defence against stowaways.
Source : https://www.irozhlas.cz/jizdenka-listek-litacka-aplikace-dpp-praha-nakup-pid