FTP unable to connect from outside

Did this ever work?

Assuming not...  Here's some basic information.  Apologies if you already know all this.

You need to configure a passive port range on the NAS.  I suggest 4 ports times the number of expected simulaneous connections.  The starting point should be >= 49152 (other values can work, but that is the expected area for private/dynamic ports).

Those ports need to be forwarded to the NAS in your router, along with port 21.

In addition, if you want to use FTP both outside and inside your LAN you will need to set masquerading off.  You'll also need an FTP client that doesn't need masquerading - FileZilla is one that works.

Finally, you'll need DDNS (or DNS if you have that) if you want reach your local network by name.  IP addresses will usually change, so you shouldn't use that.  Many home routers have built-in support for DDNS services.  Some cost, but no-ip.com still offers a free service.

I recommend FTPS (which is encrypted) for over-the-internet use, and of course you'll want a strong password.  FileZilla supports it (among other clients).