It's a shame that they don't provide any explanations. This literally means: "Over there!" Because you call for the waiter who is typically "over there". You could also call "여기요!", "over here!" to draw the waiter's attention to you "over here". This explanation would also help understanding when you could use this in other situations. If you are looking for something with a friend. And you found it, but the friend still doesn't see it, you might point at it and say "저기요!".
Odd that the hint says "hey!" but you actually type that as the answer, it's wrong.
You'd use this in a restaurant mostly to call a waiter. Not to say "hey" to a friend.
I guess the hint should be changed rather than this exercise.
i would translate this with "hey there" as in "hey, person over there; look at me!! take my order!! feed me!!"
"Excuse me" it's accurate but the app gives no context. So if you bumped someone in the street you wouldn't say this.