The connection to the FTP server is protected by the TLS security mechanism. The server FTP.DATA file contains a SECURE_LOGIN statement with either the VERIFY_USER value or the REQUIRED value. When these values are specified, the client must send a certificate to the server during the TLS authentication handshake. If the certificate is not sent, the FTP server rejects the USER command.
FTP continues.
Change the client configuration so that the client's certificate is sent to the FTP server as part of the TLS handshake. The z/OS® FTP client does not require this option because it always sends its certificate. If this reply is received by a client that cannot send a certificate, the system programmer must change the FTP server before the client can log in.
If the client cannot send a certificate, consider changing the FTP server FTP.DATA file to specify SECURE_LOGIN OPTIONAL so that a client certificate is not required.