Verifying Checksum - Operation Not Supported

param (
    # Use Generate URL function to obtain a value for -sessionUrl parameter.
    $sessionUrl = "sftp://user:mypassword;fingerprint=ssh-rsa-xx-xx-xx@example.com/",
    [Parameter(Mandatory)]
    $localPath,
    [Parameter(Mandatory)]
    $remotePath,
    [Switch]
    $pause = $False
)
 
try
{
    Write-Host $localPath -foregroundcolor Gray
 
    # Calculate local file checksum
    $localChecksum = ((CertUtil -hashfile $localPath SHA1)[1] -replace " ","")
 
    # Write-Host "Local Checksum:"
    Write-Host $localChecksum
    
    # Load WinSCP .NET assembly
    Add-Type -Path (Join-Path $PSScriptRoot "WinSCPnet.dll")
 
    # Setup session options
    $sessionOptions = New-Object WinSCP.SessionOptions
    $sessionOptions.ParseUrl($sessionUrl)
 
    $session = New-Object WinSCP.Session
 
    try
    {
        # Connect
        $session.Open($sessionOptions)
        
        Write-Host $remotePath -foregroundcolor Gray
 
        # Calculate remote file checksum
        $sha1Command = "sha1sum -b $remotePath | awk '{print `$1}'"

        $result = $session.ExecuteCommand($sha1Command)
        $result.Check()
        $remoteChecksum = $result.Output;
        
        # Write-Host "Remote Checksum:"
        Write-Host $remoteChecksum
    }
    finally
    {
        # Disconnect, clean up
        $session.Dispose()
    }
 
    # Compare cheksums
    if ($localChecksum -eq $remoteChecksum)
    {
        Write-Host
        Write-Host "Match" -foregroundcolor "green"
        $result = 0
    }
    else
    {
        Write-Host
        Write-Host "Does NOT match" -foregroundcolor "red"
        $result = 1
    }
}
catch [Exception]
{
    Write-Host $_.Exception.Message
    $result = 1
}
 
# Pause if -pause switch was used
if ($pause)
{
    Write-Host "Press any key to exit..."
    [System.Console]::ReadKey() | Out-Null
}
 
exit $result