How do I use pid recursive?

[Jake Tucker]

Can somebody help me with the correct syntax for pid-recursive?

Now that I've made an account here it's time to ask something else I'm
having trouble with.
About a year ago I started to have trouble using the pid-recursive command.
Usually on a Saturday I would for example download a Book of the Week
which had just aired Mon-Fri as a 5 parter. Each part has it's own pid
and the book also has it's own pid. Using the book pid I could
download all 5 parts with one command instead of inputting 5
individual commands in the terminal.
I can't remember what errors I was seeing when the problem started.
Since then whenever I want a book (or another example all parts of a
15 Minute Drama) I enter a pid for each part/episode. I don't do it
that often and if I was I'd of looked into this before now. I'd like
to grab the first 5 parts of the Carre book on Book at Bedtime from
the last 5 days. It is a 10 parter continuing next week. From previous
use what would happen in this situation is get_iplayer would grab the
parts that have aired and return something like not found for the
parts still to air.
The Carre book pid is b01sk4r8

I've tried:

get_iplayer --type=radio --pid-recursive=b01sk4r8
which returns:
Option pid-recursive does not take an argument

and:

get_iplayer --type=radio --pid-recursive b01sk4r8
which returns:
INFO: 0 Matching Programmes

I'm sure it was the first one I would use without any problems.
Whilst I can read the error 'Option pid-recursive does not take an
argument' I have no idea how to act on it or even if acting on it will
solve it.
What am I doing wrong (or not understanding)?
Thanks for looking.