I hesitate to sound like a broken record here, but seriously, there are some very good reasons botg and boco say the same thing *so* many times...
You have a number of issues at work here. First, you need to set a custom port range for passive mode (20 and 21 is probably not good enough and most likely what active FTP will operate on), set 50 or so ports in a high group, like 5000 or above. then ensure your router is set to forward all those ports to the computer running FZs.
second, it is very difficult to overcome router sabotage when you are connecting with a client from the same computer as the server as well routers tend to muck things up when you connect from same LAN by going out to say, No-IP to get your external address resolved then back into the LAN to try and run a session with server.
anyways, some things to try:
first make sure BPFTP server is not listening on any ports you want to use FZs on, if it uses port 21 normally shut it down as FZs cannot use it as well.
in FZs options, passive mode settings, make sure the "don't use external IP for local connections" setting is unchecked. also make sure you have set the custom port range here in the boxes- don't use ports in use by anything else, including FZs (i.e. port 21) and pick a high port number to start the range from (keeps nervous ISPs from blocking, which is common below port 1024)
if you are using FZ client to connect out to No-IP and back in to your FZs running on same machine/LAN then edit settings, connection, passive mode, and make sure the bullet is in the "Use the server's external address instead" block.
finally, before assuming FZs is at fault, slowly reread the entire
Networking Configuration, the guide already pointed to- as well, attempt to connect to your server from an actual remote IP, like a remote port forwarding proxy (I use SSH tunnels to a service for this) or use the website Tim has setup for us to use in troubleshooting and post back the logs you get from trying that.
https://ftptest.net/
also see:
Help and
FAQs oh, and there is probably countless messages in the forum on the subject too...