var sessionOptions = new SessionOptions
{
    Protocol = Protocol.Ftp,
    HostName = url,
    UserName = username,
    Password = password,
    PortNumber = 21
};
 
if (!string.IsNullOrEmpty(proxyPort))
{
    sessionOptions.AddRawSettings("ProxyHost", proxy);
    sessionOptions.AddRawSettings("ProxyPort", proxyPort);
}
 
using (var session = new Session())
{
    session.Open(sessionOptions);
 
    var transferOptions = new TransferOptions();
    transferOptions.TransferMode = TransferMode.Ascii;
 
    var transferResult = session.PutFiles(filePath, "/", options: transferOptions);
 
    transferResult.Check();
}