I just finished my first travel to Hong Kong, where I used Airport Express to move to Hong Kong station and back to the Airport. However, on the return train, I didn't find the gate to insert my card into. And thus I brought back the ticket to my country.
However, now I'm uneasy about it; it might be that I made a mistake (possibly even crime). I just followed other passengers and no one seemed to insert the card.
But is it correct to bring back the card now? For your information my ticket is one-trip, two-way one which I purchased $180 using my credit card.