i want to import a world but it allways not working.

The console prints this to me:

[22:30:04 WARN]: Could not set level chunk heightmap, array length is 0 instead of 256
[22:30:04 ERROR]: Could not pass event WorldLoadEvent to Multiverse-Core v4.1.0-b775
org.bukkit.event.EventException: null
at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:306) ~[server.jar:git-Spigot-dcd1643-e60fc34]
at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62) ~[server.jar:git-Spigot-dcd1643-e60fc34]
at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:500) [server.jar:git-Spigot-dcd1643-e60fc34]
at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:485) [server.jar:git-Spigot-dcd1643-e60fc34]
at org.bukkit.craftbukkit.v1_12_R1.CraftServer.createWorld(CraftServer.java:949) [server.jar:git-Spigot-dcd1643-e60fc34]
at org.bukkit.Bukkit.createWorld(Bukkit.java:454) [server.jar:git-Spigot-dcd1643-e60fc34]
at org.bukkit.WorldCreator.createWorld(WorldCreator.java:261) [server.jar:git-Spigot-dcd1643-e60fc34]
at com.onarandombox.MultiverseCore.utils.WorldManager.doLoad(WorldManager.java:467) [Multiverse-Core-4.1.0.jar:?]
at com.onarandombox.MultiverseCore.utils.WorldManager.addWorld(WorldManager.java:269) [Multiverse-Core-4.1.0.jar:?]
at com.onarandombox.MultiverseCore.commands.ImportCommand.runCommand(ImportCommand.java:165) [Multiverse-Core-4.1.0.jar:?]
at com.onarandombox.commandhandler.CommandHandler.checkAndRunCommand(CommandHandler.java:296) [Multiverse-Core-4.1.0.jar:?]
at com.onarandombox.commandhandler.CommandHandler.processFoundCommands(CommandHandler.java:143) [Multiverse-Core-4.1.0.jar:?]
at com.onarandombox.commandhandler.CommandHandler.locateAndRunCommand(CommandHandler.java:93) [Multiverse-Core-4.1.0.jar:?]
at com.onarandombox.MultiverseCore.MultiverseCore.onCommand(MultiverseCore.java:910) [Multiverse-Core-4.1.0.jar:?]
at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44) [server.jar:git-Spigot-dcd1643-e60fc34]
at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:141) [server.jar:git-Spigot-dcd1643-e60fc34]
at org.bukkit.craftbukkit.v1_12_R1.CraftServer.dispatchCommand(CraftServer.java:648) [server.jar:git-Spigot-dcd1643-e60fc34]
at net.minecraft.server.v1_12_R1.PlayerConnection.handleCommand(PlayerConnection.java:1399) [server.jar:git-Spigot-dcd1643-e60fc34]
at net.minecraft.server.v1_12_R1.PlayerConnection.a(PlayerConnection.java:1234) [server.jar:git-Spigot-dcd1643-e60fc34]
at net.minecraft.server.v1_12_R1.PacketPlayInChat.a(PacketPlayInChat.java:45) [server.jar:git-Spigot-dcd1643-e60fc34]
at net.minecraft.server.v1_12_R1.PacketPlayInChat.a(PacketPlayInChat.java:1) [server.jar:git-Spigot-dcd1643-e60fc34]
at net.minecraft.server.v1_12_R1.PlayerConnectionUtils$1.run(SourceFile:13) [server.jar:git-Spigot-dcd1643-e60fc34]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_252]
at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_252]
at net.minecraft.server.v1_12_R1.SystemUtils.a(SourceFile:46) [server.jar:git-Spigot-dcd1643-e60fc34]
at net.minecraft.server.v1_12_R1.MinecraftServer.D(MinecraftServer.java:748) [server.jar:git-Spigot-dcd1643-e60fc34]
at net.minecraft.server.v1_12_R1.DedicatedServer.D(DedicatedServer.java:406) [server.jar:git-Spigot-dcd1643-e60fc34]
at net.minecraft.server.v1_12_R1.MinecraftServer.C(MinecraftServer.java:679) [server.jar:git-Spigot-dcd1643-e60fc34]
at net.minecraft.server.v1_12_R1.MinecraftServer.run(MinecraftServer.java:577) [server.jar:git-Spigot-dcd1643-e60fc34]
at java.lang.Thread.run(Thread.java:821) [?:1.8.0_252]
Caused by: java.lang.IllegalArgumentException: ChunkNibbleArrays should be 2048 bytes not: 0
at net.minecraft.server.v1_12_R1.NibbleArray.(NibbleArray.java:14) ~[server.jar:git-Spigot-dcd1643-e60fc34]
at net.minecraft.server.v1_12_R1.ChunkRegionLoader.a(ChunkRegionLoader.java:402) ~[server.jar:git-Spigot-dcd1643-e60fc34]
at net.minecraft.server.v1_12_R1.ChunkRegionLoader.a(ChunkRegionLoader.java:94) ~[server.jar:git-Spigot-dcd1643-e60fc34]
at net.minecraft.server.v1_12_R1.ChunkRegionLoader.loadChunk(ChunkRegionLoader.java:72) ~[server.jar:git-Spigot-dcd1643-e60fc34]
at org.bukkit.craftbukkit.v1_12_R1.chunkio.ChunkIOProvider.callStage1(ChunkIOProvider.java:1) ~[server.jar:git-Spigot-dcd1643-e60fc34]
at org.bukkit.craftbukkit.v1_12_R1.util.AsynchronousExecutor.skipQueue(AsynchronousExecutor.java:336) ~[server.jar:git-Spigot-dcd1643-e60fc34]
at org.bukkit.craftbukkit.v1_12_R1.util.AsynchronousExecutor.getSkipQueue(AsynchronousExecutor.java:295) ~[server.jar:git-Spigot-dcd1643-e60fc34]
at org.bukkit.craftbukkit.v1_12_R1.chunkio.ChunkIOExecutor.syncChunkLoad(ChunkIOExecutor.java:16) ~[server.jar:git-Spigot-dcd1643-e60fc34]
at net.minecraft.server.v1_12_R1.ChunkProviderServer.getChunkAt(ChunkProviderServer.java:137) ~[server.jar:git-Spigot-dcd1643-e60fc34]
at net.minecraft.server.v1_12_R1.ChunkProviderServer.getChunkAt(ChunkProviderServer.java:120) ~[server.jar:git-Spigot-dcd1643-e60fc34]
at net.minecraft.server.v1_12_R1.ChunkProviderServer.getChunkAt(ChunkProviderServer.java:116) ~[server.jar:git-Spigot-dcd1643-e60fc34]
at org.bukkit.craftbukkit.v1_12_R1.CraftWorld.getChunkAt(CraftWorld.java:138) ~[server.jar:git-Spigot-dcd1643-e60fc34]
at org.bukkit.craftbukkit.v1_12_R1.CraftWorld.getBlockAt(CraftWorld.java:95) ~[server.jar:git-Spigot-dcd1643-e60fc34]
at org.bukkit.craftbukkit.v1_12_R1.CraftWorld.getBlockAt(CraftWorld.java:568) ~[server.jar:git-Spigot-dcd1643-e60fc34]
at com.onarandombox.MultiverseCore.utils.SimpleBlockSafety.playerCanSpawnHereSafely(SimpleBlockSafety.java:84) ~[?:?]
at com.onarandombox.MultiverseCore.MVWorld.readSpawnFromWorld(MVWorld.java:423) ~[?:?]
at com.onarandombox.MultiverseCore.MVWorld.(MVWorld.java:82) ~[?:?]
at com.onarandombox.MultiverseCore.MVWorld.(MVWorld.java:59) ~[?:?]
at com.onarandombox.MultiverseCore.utils.WorldManager.doLoad(WorldManager.java:477) ~[?:?]
at com.onarandombox.MultiverseCore.utils.WorldManager.doLoad(WorldManager.java:448) ~[?:?]
at com.onarandombox.MultiverseCore.utils.WorldManager.doLoad(WorldManager.java:423) ~[?:?]
at com.onarandombox.MultiverseCore.utils.WorldManager.loadWorld(WorldManager.java:404) ~[?:?]
at com.onarandombox.MultiverseCore.listeners.MVWorldListener.loadWorld(MVWorldListener.java:57) ~[?:?]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_252]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_252]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_252]
at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_252]
at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:302) ~[server.jar:git-Spigot-dcd1643-e60fc34]
... 29 more

For 1.12.x, you will need to use an older version of Multiverse for it to work. Multiverse 2.5.0 should work: https://dev.bukkit.org/projects/multiverse-core/files/2428161

Okay i will try it some time later, but thank you ^^

For 1.12.x, you will need to use an older version of Multiverse for it to work. Multiverse 2.5.0 should work: https://dev.bukkit.org/projects/multiverse-core/files/2428161

That version nicegamer7 link should work. You also need to ensure the world you need to import is of the same mc version as your server. If you still have issues, you can reopen this or ask in our discord https://discord.gg/NZtfKky