"Are you against me?"
Translation:Είσαι εναντίον μου;
We'll need a bit more clarification. From the answer shown at the top of this page I see only singular Greek and a review of the incubator show the singular Greek as the preferred version with the plural as an alternative.
So, of course, the singular, should have been accepted. Please tell us where you had this.. on the web, Android or iOS? What kind of exercise was it...Strengthen skills, translation from En to Gr etc? that will help us find a solution to this.
The hints are like a dictionary; many words may be shown but not all are correct in each situation. On the Duo Drop Down Hints it's usually the top hint that fits each sentence. Duo does that so to make it easier for you. In this case "εναντίον μου" is shown first.
You can say for example: Αντίθετα με μένα...unlike me...