If you bought something that was marked 'free return shipping' (generally clothing), then the reason doesn't matter; it will be free.
Not only that, if you bought something that doesn't have free return shipping all you need to do is make it seem that it was amazons fault you are returning it (EG: for the return reason choose "description did not match item") and you will get a free return label. If you morals don't let you do that
then chat in and say you would like to return it and they will almost always create the return for you and send you the free label. I've done the latter many times but it can only be done for items sold by amz.