To explain further look at the topic. Its number is 1001
So we need to use a shortcode to manipulate the To header in the call, which is what the funky shortcode does.
If we dial 11001, the system actually dials 2099, but alters the To field in the invite to what was dialled by the user/ipo.
Take a look at the shortcode now, pay particular attention to the telephony number field: 2099|>>.
Put very simply, it tells the system to call 2099 and change the To header to be what was dialled (the . grabs all entered digits from the code field and sets the To header to this)
So with the existing shortcode, we are sending 11001 to IPOCC because the shortcode is required 5 digits. Its not a recognised topic number so the call is rejected.
Theoretically, you could change the shortcode to be:
1XXXX / Dial Extn / 2099|>>N
This would only use the 4 X's and drop the leading 1, but unless there is a specific reason for there being 5 digit shortcodes and 4 digit topics, it'd just be easier to setup the shortcode the way it's meant to be from the outset.
Just wanted to explain the theory behind me saying the shortcode is wrong.
