Check this thread which discusses some of the prerequisites for SWD. Setting up Software Distribution
A copy of the client logs would be handy, and L2 should be asking for that on your support case.
If I had to guess, I’d bet that the SWD Download Plugin needs to be registered on your root server. I think the Manage Software Deployment Dashboard would say this…but I wonder if it may not report the prereq correctly if your Root server is not subscribed to the Software Deployment site? Not sure though because I’d expect the action status wouldn’t say “cached on server”, but maybe worth checking.