When trying to connect by FTP with FileZilla (for example) you get something like this, with xxx.xxx.xxx.xxx replaced by your server IP and yyyy by your ftplogin
Status: Connecting to xxx.xxx.xxx.xxx:21...
Status: Connection established, waiting for welcome message...
Response: 220 ProFTPD 1.3.3g Server (Sentora FTP Server) [::ffff:xxx.xxx.xxx.xxx]
Command: USER yyyy
Response: 331 Password required for zadmin
Command: PASS ********
Error: Could not connect to server
1) Ensure your login and password matches those who created defined in Sentora.
Note that Sentora is not creating any default FTP account, you have to create one.
2) Ensure that the home directory assigned to the FTP account is reachable to proftpd : check its owner and group, and its access rights. (If you created it manually, there is some chance that you would be the owner of the directory and that proftpd cannot access it).