Edit:
HostName PortNumber UserName Password SshHostKeyFingerprint $localPath $remotePath $archivePath

# Load WinSCP .NET assembly (must be in same folder as this script or in PATH)
Add-Type -Path "WinSCPnet.dll"

# === Session settings ===
$sessionOptions = New-Object WinSCP.SessionOptions -Property @{
    Protocol              = [WinSCP.Protocol]::Sftp
    HostName              = "hostname.server.tld"
    PortNumber            = 22
    UserName              = "username"
    Password              = "password"
    SshHostKeyFingerprint = "ssh-rsa 4096 FingerprintFingerprintFingerprint"
}

$localPath   = "C:\Nieuw"
$remotePath  = "/in"
$archivePath = "C:\Archief"
$logFolder   = "C:\WinSCP"

# === Logging function with weekly rotation and cleanup ===
function Write-Log {
    param([string]$message)

    $now = Get-Date
    $year = $now.Year
    $week = [math]::Floor(($now.DayOfYear - 1) / 7) + 1
    $currentLogFile = Join-Path $logFolder ("SftpWatcher_{0}-W{1}.log" -f $year, $week)

    $timestamp = $now.ToString("yyyy-MM-dd HH:mm:ss")
    $entry = "$timestamp - $message"

    Add-Content -Path $currentLogFile -Value $entry
    Write-Host $entry

    # Cleanup old log files (>30 days)
    Get-ChildItem -Path $logFolder -Filter "SftpWatcher_*.log" | Where-Object {
        $_.LastWriteTime -lt (Get-Date).AddDays(-90)
    } | Remove-Item -Force
}

# === Upload and move function ===
function Upload-File {
    param([string]$filePath)

    $name = [System.IO.Path]::GetFileName($filePath)

    if (!(Test-Path $filePath)) {
        Write-Log "Skipped (not found): $filePath"
        return
    }

    try {
        $session = New-Object WinSCP.Session
        $session.Open($sessionOptions)

        Write-Log "Uploading $name ..."
        $transferResult = $session.PutFiles($filePath, "$remotePath/$name")
        $transferResult.Check()

        Write-Log "Uploaded $name successfully."

        # Move file to archive folder
        $destFile = Join-Path $archivePath $name
        Move-Item -Path $filePath -Destination $destFile -Force
        Write-Log "Moved $name to archive folder."
    }
    catch {
        Write-Log ("Error uploading " + $filePath + ": " + $_.ToString())
    }
    finally {
        if ($session -ne $null) {
            $session.Dispose()
            Write-Log "Disconnected."
        }
    }
}

# === Initial sync at startup ===
Write-Log "SFTP Watcher starting. Checking existing files in $localPath ..."
Get-ChildItem -Path $localPath -Filter "*.*" -File | ForEach-Object {
    Upload-File $_.FullName
}

# === Folder watcher for new files ===
$watcher = New-Object System.IO.FileSystemWatcher
$watcher.Path = $localPath
$watcher.Filter = "*.*"
$watcher.IncludeSubdirectories = $false
$watcher.EnableRaisingEvents = $true

$createdEvent = Register-ObjectEvent $watcher Created -Action {
    $file = $Event.SourceEventArgs.FullPath
    Write-Log "New .eee file detected: $file"
    Start-Sleep -Seconds 5   # wait if file is still being written
    Upload-File $file
}

Write-Log "SFTP Watcher is now monitoring $localPath."

# === Keep-alive loop with graceful exit ===
try {
    while ($true) {
        Start-Sleep -Seconds 10
    }
}
finally {
    # Cleanup watcher and events
    if ($createdEvent) { Unregister-Event -SourceIdentifier $createdEvent.Name }
    if ($watcher) { $watcher.Dispose() }
    Write-Log "SFTP Watcher service stopped."
}

Install service using Non-Sucking Service Manager:

nssm.exe install WinSCPFolderWatcher