Authentication servers are down. Please try again later, sorry!

I am trying to set up a spigot server off a spare laptop that I have converted to ubuntu, but for whatever reason I get the error in the title when I try to connect off my Windows 10 PC.

Here are logs of the errors:

Spoiler: Error 1.

[13:00:06] [User Authenticator #1/INFO]: Disconnecting [email protected][id=,name=USER,properties={},legacy=false] (/192.168.0.20:60735): Authentication servers are down. Please try again later, sorry!
[13:00:06] [User Authenticator #1/ERROR]: Couldn't verify username because servers are unavailable
[13:00:06] [Server thread/INFO]: [email protected][id=,name=USER,properties={},legacy=false] (/192.168.0.20:60735) lost connection: Authentication servers are down. Please try again later, sorry!

Username redacted as USER.

Spoiler: Error from friends.

io.netty.channel.AbstractChannel$AnnotatedConnectException: Connection refused: no further information:

I have tried updating certificates, I have opened all ports (I don't think my ISP lets me but I am connecting over LAN so it shouldn't matter.

Another detail, if I set the server to offline mode, it allows me to join. No I am not using a cracked account.
Time zones on both computers are set to my local, to no avail.
server-ip is blank, I've tried with internal and external IP's just messing around.

EDIT: Do I need a specific version of java installed?
UPDATE: I configured an IP Passthrough, so no ports should be closed, however the same error occurs.

 

Bump. not solved yet.