this call works just fine
/MCWS/v1/Playback/PlayByFilename?Filenames=http://dreamsiteradiocp4.com:8046/stream
is this working by accident or PlayByFilename deliberately supports playback of arbitrary URLs?
this is actually a nice feature to have though I'd suggest it should be a different api call, i.e. something like PlayURL and don't allow PlayByFilename to do that as it's fairly surprising behaviour