Simulate a SIP Phone request for config

I am having issues with the config for a sip phone (Aastra 6737i) and would like to manually download the config and look at it.

The basic settings I have are - directly from the phone;
  Download Protocol - Http
  HTTP Server - FQDN
  HTTP Path - aastra6737i
  HTTP Port - 80

I also know the MAC address of the phone and the SIP Username and Password

After some reading, I tried to use the Powershell "invoke-webrequest" command to download the file.

I have tried two different ways to pass the Username & Password.
Please Note - I did not write this code, but copied it from examples I found substituting my SIP username and Password

Method One
        $username = "username"
        $password = "password" | ConvertTo-SecureString -asPlainText -Force
        $cred = New-Object System.Management.Automation.PSCredential($username,$password)
        invoke-webrequest -outfile mac.cfg http://fqdn/aastra6737i/mac.cfg -Credential $cred

Method Two
       $user = 'username'
       $pass = 'password'

       $pair = "$($user):$($pass)"

       $encodedCreds = [System.Convert]::ToBase64String([System.Text.Encoding]::ASCII.GetBytes($pair))

       $basicAuthValue = "Basic $encodedCreds"

       $Headers = @{
             Authorization = $basicAuthValue
        }
        invoke-webrequest -outfile mac.cfg http://fqdn/aastra6737i/mac.cfg -Headers $Headers

 === Again I did not write these scripts, and I am NOT a programmer.

However regardless of the script I get;
     invoke-webrequest : Forbidden
     You don't have permission to access /aastra6737i/mac.cfg on this server.


I know the file name "mac.cfg" that I am trying to download is correct


Does anyone know how a SIP phone contacts, authenticates and then downloads it config file and how this could be accomplished manually/programmably.


Thank you



Very much appreciated.