I tried connecting my laptop to a VPN outside of my network, and I am able to accept the certificate, but again, same error. I also have port 21 and the passive ports forwarded on my router. I tried going to System > Network > Firewall and I created some Accept rules for port 21 and the passive ports (I had seen this post, and example_rules.jpg), but it makes no difference. The client instructs the server to work with FTP. I have a Mac, with 8GB RAM and am using Rcon. The client sends an FTP PORT command that talks about using the active FTP mode, its IP address, and also the port number for establishing a data connection to which the server will connect. But, if others try, it says 'Cant connect: connection refused: connect'. I tried testing the connection with Filezilla installed on my laptop (on the same network with Odroid), and it authenticates fine, and I can even accept the certificate, but then I get the error, ' The data connection could not be established: ECONNREFUSED - Connection refused by server.' My Minecraft Server is running perfectly and I can connect. I followed these directions to have what I think are the right settings for FTP. I intend to connect outside of my network. I have enabled FTP under Services, and have also created a certificate and enabled SSL/TLS connections. I have an Odroid HC2 with OMV 4 installed.

Mac ftp server connection refused