[FFmpeg-user] converting aax to mp3

[Mary Strimel]

Hello,
I am trying to convert Audible AAX file to mp3 using the same method
found here https://ffmpeg.org/pipermail/ffmpeg-user/2016-January/029880.html

I am getting the same error as the OP but cannot seem to solve it.

ffmpeg -activation_bytes xxxxxx sample.aax -vn -c:a copy sample.mp4a

throws the error "Unrecognized option -activation_bytes"

I am filling in the xxxxxx with the authcode that I retrieved from
Audible using the available tools.
What should I do?
Thanks.