This question already has an answer here:
It's hard to explain the situation in title, so here it is:
I'm booking a 2 ways tickets from Singapore to Vietnam (Hanoi). However, i didn't board the trip Sing-Viet. Instead, I purchased another 1 way ticket, from Singapore to Vietnam with different time.
In that case, when I'm back from Vietnam to Singapore, the flight counter said, my tickets is not valid anymore, as i didn't take the 1st board,
Based on International Rules, they said.
So, Is my 2 ways tickets valid?