Perl POST to workitem factory URI returns 404 - why?

Hi all, this is for CLM 4.0.7 iFix007 using WAS 8.5.5.3 on Windows Server 2008 R2.

I'm trying to create a workitem using Perl and a combination of REST and OSLC calls.  I think my RDF structure looks OK but the POST call to the creation factory URI returns 404 no matter how I tweak the code.  I rigure that if my RDF structure is wrong, I'll an error returned but it won't be 404. 

The endpoint URI matches the format in https://jazz.net/wiki/bin/view/Main/ResourceOrientedWorkItemAPIv2#Creating_Work_Items (URL="https://localhost:9443/jazz/oslc/contexts/_9BHm0EqVEd6HXO10niqZpg/workitems"): https://<server>:9443/jazz/oslc/contexts/_xohRkQKWEeS1oId-vRdUPQ/workitems

$request = HTTP::Request->new(POST => $endpoint);
$request->header('Content-Type' => 'application/rdf+xml');
$request->header('Accept' => 'application/rdf+xml');
$request->header('OSLC-Core-Version' => '2.0');
$request->content($requestData);

$response = $userAgent->request($request);

However using that URI in a browser returns 'SRVE0255E: A WebGroup/Virtual Host to handle devccm.nbsnet.co.uk:9443 has not been defined.'

According to all the docs I can find the URI should be good, so I'm wondering what I've missed.  Is there something in the WAS config, for example?

If someone can offer some advice or a working example I'd be grateful.  I'm happy to share the code I have if that would help.