FZ server only works locally

[XistenZ]

All necessary ports are forwarded, the firewall lets everything through, but I can't connect from outside the local network.
All I can find about this issue has to do with ports and firewalls,what else makes the server only work locally?

[boco]

How did you test? Please always use our test facility https://ftptest.net for such tasks.

what else makes the server only work locally?

For example, dumb ISPs who don't offer a true public IPv4 anymore but place you behind corporate NAT. It could also be that you run on an IPv6 transition connection like DS-Lite (which also doesn't provide a real IPv4). Then, you can't run servers on IPv4 at all.