"They are friends."
Translation:Αυτοί είναι φίλοι.
As far as I know, Duo does not reject answers for misplaced accents (unless the word changes meaning maybe, e.g. πως vs πώς, but I'm not sure that actually happens). That means there might be another mistake that was not as obvious. Many typos cause an answer to be rejected, as does a mix of Latin and Greek alphabet characters, even if they look similar. In such cases it's helpful to take a screenshot and post it here - we have no other way of seeing your answers. :)