anyone use CURL.exe from Windows env to access ARS SPML ? seeing issue with auth

I used a script to confirm availability of the SPML provider and operational status by returning attributes of an object from all 4 configured ARS  SPML hosts.

Powershell query to return data works ... however the customer team uses VMWare Orchestration software that appears to use curl under the covers.

They can hit primary SPML host, but when it becomes unavailable, they need the secondary SPML host to provide the service.

I have managed to re-produce the error message from one of my SPML hosts in another geo location - but don't understand the local failure here.

SPML host 1 returns data as long as the service is up for both powershell and curl based query
SPML host 2 returns data when queried via PS script (below) but not using the orchestration client 'curl backend'

this is the error returned, where the issue is encountered - keeping in mind: famous last words .... these servers are all setup identically, IIS running with same pool identity, same permissions granted.  

Are any ARS birdies out there leveraging CURL for monitoring ... working well, or even returning SPML results that works via PS> but fails via CURL?

test-ARSspml myserver1

myserver1 - Unable to access SPML on this host The request failed with HTTP status 401: Unauthorized.

 function test-ARSspml()
   {  if(!($query = $args[0]))
        { $curName = [system.environment]::UserName
          $curObjName = ([adsisearcher]"name=$curName").findone().properties.distinguishedname
        }else{$curObjName = ([adsisearcher]"name=$query").findone().properties.distinguishedname
     foreach($spmlhost in ('myServer1','myserver2','myServer3','myServer4'))
     {  try{  $global:ARSOAP = New-WebServiceProxy -Uri https://$($spmlhost)/ARServerSPML/SPMLProvider.asmx `
                                            -usedefaultcredential  `
                                            -ErrorVariable iFailed `
                                            -erroraction  silentlycontinue
              $ARSOAP.PreAuthenticate = $true
              $Type = $ARSOAP.GetType().Namespace
              $LookupRequest = New-Object -TypeName ($type + ".CLookupRequest")
              $CPSOID = New-Object -TypeName ($Type + ".CPSOID")
              $CPSOID.ID = $curObjName
              $LookupRequest.psoID = $CPSOID
           if($ARSOAP.lookup($LookupRequest).status -eq 'failure')
             }else{if($found = ($ARSOAP.lookup($LookupRequest)
                     {$found |select @{name='server';e={$spmlhost}},
          }catch{"$spmlhost - Unable to access SPML on this host $ifailed"}