"Vil du ikke lave en sandwich til mig?" is a perfectly natural sentence in Danish, but the word 'ikke' puzzles many foreigners. You can to interpret it as a plea: 'Vil du ikke holde op med at slå mig' (would you please stop beating me). So, Duo is wrong in putting the 'not' into the English sentence. 'Will you make me a sandwich, please' would be my best translation (as a native Dane).