Sample code required for Invoke-RestMethod using HTTPS and Basic Authorisation

I'm trying to use powershell V3 to play with a HTTPS restful API but am having difficult connecting to it!

I used FireFox's RESTClient to verify I'm using correct API calls and basic authorisation headers.

When I transfer the same calls into Powershell it fails to connect :(

my code:

# This nugget should help me to get around any self-signed certificate issues I believe
$netAssembly = [Reflection.Assembly]::GetAssembly([System.Net.Configuration.SettingsSection])
 
if($netAssembly)
{
    $bindingFlags = [Reflection.BindingFlags] "Static,GetProperty,NonPublic"
    $settingsType = $netAssembly.GetType("System.Net.Configuration.SettingsSectionInternal")
 
    $instance = $settingsType.InvokeMember("Section", $bindingFlags, $null, $null, @())
 
    if($instance)
    {
        $bindingFlags = "NonPublic","Instance"
        $useUnsafeHeaderParsingField = $settingsType.GetField("useUnsafeHeaderParsing", $bindingFlags)
 
        if($useUnsafeHeaderParsingField)
        {
          $useUnsafeHeaderParsingField.SetValue($instance, $true)
        }
    }
}

[System.Net.ServicePointManager]::ServerCertificateValidationCallback = {$true}

$username = 'XXX'
$upassword = 'XXX'

$auth = $username + ':' + $upassword

$Encoded = [System.Text.Encoding]::UTF8.GetBytes($auth)
$EncodedPassword = [System.Convert]::ToBase64String($Encoded)

$headers = @{"Authorization"="Basic $($EncodedPassword)"}

Invoke-RestMethod -Uri https://192.168.5.3:8444/csa/rest/login/CSA-Provider/admin -Header $headers -Method Get

The first time this is run I get the following error :

PS C:\Users\landg> C:\Users\landg\Documents\Scripts\CSA API\CSA_API_DEMO_take5.ps1
Invoke-RestMethod : Unable to connect to the remote server
At C:\Users\landg\Documents\Scripts\CSA API\CSA_API_DEMO_take5.ps1:35 char:1
+ Invoke-RestMethod -Uri https://192.168.5.3:8444/csa/rest/login/CSA-Provider/admi ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (System.Net.HttpWebRequest:HttpWebRequest) [Invoke-RestMethod], WebException
    + FullyQualifiedErrorId : WebCmdletWebResponseException,Microsoft.PowerShell.Commands.InvokeRestMethodCommand

And all subsequent runs produce this error :

PS C:\Users\landg> C:\Users\landg\Documents\Scripts\CSA API\CSA_API_DEMO_take5.ps1
Invoke-RestMethod : The underlying connection was closed: An unexpected error occurred on a send.
At C:\Users\landg\Documents\Scripts\CSA API\CSA_API_DEMO_take5.ps1:35 char:1
+ Invoke-RestMethod -Uri https://192.168.5.3:8444/csa/rest/login/CSA-Provider/admi ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (System.Net.HttpWebRequest:HttpWebRequest) [Invoke-RestMethod], WebException
    + FullyQualifiedErrorId : WebCmdletWebResponseException,Microsoft.PowerShell.Commands.InvokeRestMethodCommand

I've run out of things to try but feel certain it's a security/certificate issue with my setup.

I also noticed when I go back to basics that this also produces the same error - 

Invoke-WebRequest -Uri https://www.google.co.uk -Method Get

but works if I use HTTP://

All suggestions would be greatly appreciated.

Kind Regards,

Graham.