I just recently installed MineOS Turnkey on Oracle VirtualBox and got the server all configured but when I try to join using 127.0.0.1 or the local ip for the server I get this error, I even tried using my external ip and the same thing happens.
(https://gyazo.com/48187232815542b5a3cb88d2435ec6e6)
127.0.0.1 means localhost–the machine that the server itself is running on. That refers to a different machine from your desktop client (which also has 127.0.0.1), so attempting to connect from desktop via 127.0.0.1 won’t work. You’d instead connect to an IP on your server that is on the same network as your desktop (remember, even virtual servers on that desktop aren’t local just because!)
In 99/100 cases with MineOS in residential deployments, you’ll need to set your Virtualbox to get an IP address in the same network as your router; often, this means using Bridged Networking.
You also won’t use your external IP address, because your server does not have that external IP address–your router does. In most cases, you’d use your external IP address if you’re NOT on your home network, and you’ll also have to implement “port forwarding” to connect from outside your home network. (but this isn’t as critical yet).
TL;DR you’re probably going to get this working by connecting to a Minecraft server hosting on 192.168.0.x (or whatever network your router uses; make Virtualbox get a 192.x.x.x address).