$InsightServerUrl = "Your Site URL Here"
$Username = "Your Case Sensitive Username"
$Password = "Your API KEY Here"

# Encode Creds
$auth = $Username + ':' + $Password
$Encoded = [System.Text.Encoding]::UTF8.GetBytes($auth)
$authorizationInfo = [System.Convert]::ToBase64String($Encoded)

# Set headers with ExperimentalApi
$Headers = New-Object 'System.Collections.Generic.Dictionary[[String],[String]]'
$Headers.Add('content-type' , 'application/json')
$Headers.Add('Authorization', 'Basic ' + $authorizationInfo)
$Headers.Add('X-ExperimentalApi', 'opt-in')

# Call the URI
$Request = [System.UriBuilder]"$InsightServerUrl/rest/servicedeskapi/insight/workspace"
$response = Invoke-RestMethod -Uri $Request.Uri -Headers $headers -Method GET
$response.values.workspaceId