IP server

Hello,I have a problrm with IP servers.On 1.15.2 I play and doesn't works,1.8 and 1.7.5 I also tried and it doesn't work.The server is "cubecraft",i tried:play.cubecraft.net; play.cubecraftgames.net and other servers and doesn't work.What's happening?When I try to login server writes:not authenticated with Minecraft.net.What to do?