In this particular situation you don't have any clue listening to the audio. "amis" and "amies" should both be accepted, don't you think?
The dictation exercise was disabled so you should not have been requested to "type (in French) what you hear ( in French)."
Why isn't my answer accepted? "Our friends are writing some books". Is there an alternate way to express my answer?
I think that your answer is correct. It should be reported so that it can be added to the list of acceptable answers.