Failure in attempting to combine mp3 or m4b files into a single m4b audio book

[instrumentally]

I have tried using version 6.5.2 for more than a dozen times, trying to create a single m4b audiobook from multiple mp3 or m4b files. Every attempt has been a failure. All you get are 12 m4b files if you start with 12 mp3 files. If you start with 12 m4b files, you end up with 12 more m4b files. You will never get a single m4b containing the chaptered files. Here's a video showing how this process fails: https://www.youtube.com/watch?v=16I68RS_LWw What am I doing wrong? I really don't get the point of this app.

[mrg666b]

Go to quality and try setting to iPhone, it should merge all files I had it on legacy, but it kept not joining them I changed to iPhone, and it's OK I suppose anything except legacy might work