how can I hear the difference between "amies" and "amis"
you can't. It will depend on the context.
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?
And they are both accepted.
"amis" was not accepted just now.
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.
why isn't "nos amis écrivent des livres" a good answer?
Same problem - why aren't amis and amies both accepted?
report it, mine (Ami) was rejected too
Still not accepting 'nos amis'
Nos amies flip des burgers
My friends are male