System.Net.WebException: The request failed with HTTP status 400: Bad Request.~~ at Microsoft.UpdateServices.Administration.AdminProxy.CreateUpdateServer(Object args)~~ at Microsoft.SystemsManagementServer.WSUS.WSUSServer.ConnectToWSUSServer(String ServerName, Boolean UseSSL, Int32 PortNumber)
SCCM SUP and WSUS sync failed -> If you are seeing SCCM SUP and WSUS sync failed in WSUSCTRL.log then you need to make sure IIS is installed correctly in the WSUS server.
To verify you need to open IIS on the WSUS server and browse some IIS components like below.
If the page is not opening properly then you need to check IIS Role-> Features where have installed all roles and features are not specially Directory Browsing .
Reinstalled the missing components and did the proper binding and checked again it should work.
I fixed my similar issue after following similar steps