Note that the ftps:// prefix commonly refers to an implicit mode FTP over TLS/SSL. The .NET framework supports only an explicit mode. Though even if your URI is indeed referring to the implicit mode, most servers would support the explicit mode too anyway. So this won't be a problem typically. For the explicit mode, ftpes:// is sometimes used.

sftp|ftp|ftps|ftpes|http|https|scp :// [ <username> [ : <password> ] [ ; <fingerprint> ] @ ] <host> [ : <port> ] /

You should also always explicitly specify a protocol (sftp, ftp, scp, for FTP over implicit TLS/SSL use ftps, for FTP over explicit TLS/SSL use ftpes, for WebDAV use http, for WebDAV over TLS/SSL use https).1) For all protocols WinSCP-specific alternative is supported, with winscp- prefix.

For a client to connect to a server using SSL, then the host for that connection needs to be set to FTPS. In FileZilla client this means prefixing the host with "FTPES://" for "explicit" FTPS, or "FTPS://" for the legacy "implicit" FTPS.