The 'ProtocolVersion'
error typically means that the client and server uses different versions of the TLS protocol.
The TLS protocol version can be set using the Ftp.Settings.SslAllowedVersions
property.
By default, TlsVersion.TLS12
is included. However, it seems you explicitly disabled it byt setting the Ftp.Settings.SslAllowedVersions
property to a lower version(s).
To make your code working, either don't modify the Ftp.Settings.SslAllowedVersions
property or enable TLS 1.2 like this:
var client = new Ftp();
client.Settings.SslAllowedVersions = TlsVersion.TLS12;