"Everyone has to die."
Translation:Todo el mundo tiene que morir.
If you don't want to use "todo el mundo" for "everyone," Duo usually accepts "todos." Todos tienen que morir.
"Todo" by itself usually means "everything."
DL needs to be corrected. Everyone has to die doesn't always mean everyone in the world.
Did you leave out the "que"? Sometimes when you miss part of the preferred answer, they give you a completely different answer instead of correcting you to what they are using as the preferred answer on the discussion page. You can always look here to see how your answer was wrong.