FTP Server connection closed

Hi All,

I'm new to macOS Server and the FTP server. If performing a local network connection the FTP server works and allows me to login, however when connecting via internet the FTP server closes the connection with an 421 service not available error.

Based in the UK using Virgin Media as my service provider, virgin hardware is set to modem mode, this is connected to Apple Extreme v2 acting as a router with the FTP ports 20, 21, 22 open.

Secure connection SSH is selected in the server app.

The FTP server is running.

What am i missing ?

The Server app shows that the ports are open on the router.