Should this be a return ticket rather than round trip? Does the ticket take one in a loop back to one's destination in one go? If so it is round trip.
"Round-trip ticket" means that the same as "return ticket" even if you find the latter more logical. Both terms should be accepted.
The Romanian is similar to the French: "aller-retour."
"return" = BrE
"round trip" = AmE
It's a return ticket. It's the same in Italian: "andata e ritorno"
"My ticket is a return" (British English) accepted. Like most DL courses, this one uses American English, hence "round trip".
I agree with Coriander. A round trip is exactly that (eg, Bucharest, Sibiu, Brasov, Bucharest), not a return. However, thank you so much, Duolingo, I no longer have to write "two-way"!