Vivecraft connecting to vanilla, invalid session

[Pure_Fyre]

Hi,
I tried to connect to a vanilla 1.14.4 spigot server. It refused my connection, telling me I had an invalid session. My only JVM argument is -Xmx4G.
What does the server owner or myself need to do in order to allow me to connect, preferably without forcing other players to install anything.
Thank you!

[jrbudda]

That means the server is not in offline mode and you are not logged into your mojang account.