FTP: The data connection could not be established: ECONNREFUSED - Connection refused by server

I have an Odroid HC2 with OMV 4 installed. I have enabled FTP under Services, and have also created a certificate and enabled SSL/TLS connections. I intend to connect outside of my network. I followed these directions to have what I think are the right settings for FTP. 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."

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. I also have port 21 and the passive ports forwarded on my router. I get the same error locally. 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 honest to goodness have no idea what I'm doing. Please help.

I don't think I forwarded the passive ports properly in my router, so I fixed that, and now I'm getting a new error:

GnuTLS error -110: The TLS connection was non-properly terminated.

I don't even know what I did, but I could start connecting and I could see my shared folder. I couldn't write to the folder (even though I allowed read/write through privileges, not acl). So then I created a shared folder from the ftp settings, and then suddenly I am getting the connection refused error again. WHY?

Somehow port 21 magically changed to port 22. I can connect again. However, I still can't transfer a file to the server. I get permission denied. I have tried adding the user I created to the group "sftp-access," but it's not helping.

Everything is working now. Note entirely sure why, but it was a lot of trial and error. I created a tutorial here.