It's probably a firewall that blocks the transfer connection.

Thanks for that. I have managed to get this working.
Now I have another problem. I have used it on a production server now I get an error:

Transfer channel can't be opened. Reason: No connection could be made because the target machine actively refused it.

If I use WinSCP directly on that same server to upload a file it works as expected, but when I run the same PutFile through the code I get the above error. Do you know what could be wrong? Thanks a lot.

The easiest solution is to configure the session in WinSCP GUI and have WinSCP generate the code for you.

See
https://winscp.net/eng/docs/ui_generateurl
https://winscp.net/eng/docs/guide_filezilla_automation
https://winscp.net/eng/docs/rawsettings

Hi. I'm trying to use your .NET C# library for uploading files to FTP through proxy. I don't know how should I set the proxy settings. The FileZilla settings works as on the attached screen.

Could you please help me.
Thanks