When i created a minecraft server trough forge and hamachi to play with my friend its keep crashing, its says [18:14:18] [Server thread/WARN] [avatarmod]: [Warn/BAD_CLIENT_PACKET] Player RairisGamingSK: Unexpected data, Sent request data for a player with account 'cf88d8f4-915c-42aa-afbf-377bc9caa6f2', but that player is not in the world.

Have you tried updating your forge?

The mod requires 1.12.... this happens to me and I have the latest version of 1.12.

Is your server cracked/in offline mode?

#167 Well, I can say that for me, I'm premium and bought my account and have the same issue.

Actually, misread the crashlog at first. You need to update Forge.

and then it crashes

In crash reports its says
---- Minecraft Crash Report ----
// This doesn't make any sense!

Time: 4.6.2020 18:04
Description: Exception in server tick loop

java.lang.NoSuchMethodError: net.minecraftforge.fml.relauncher.ReflectionHelper.getPrivateValue(Ljava/lang/Class;Ljava/lang/Object;Ljava/lang/String;Ljava/lang/String;)Ljava/lang/Object;
at com.crowsofwar.avatar.common.util.AvatarUtils.(AvatarUtils.java:61)
at com.crowsofwar.avatar.common.data.BendingData.writeToNbt(BendingData.java:511)
at com.crowsofwar.avatar.common.data.AvatarPlayerData.writePlayerDataToNBT(AvatarPlayerData.java:81)
at com.crowsofwar.gorecore.data.PlayerData.writeToNBT(PlayerData.java:128)
at com.crowsofwar.gorecore.data.PlayerData$1.writeV(PlayerData.java:61)
at com.crowsofwar.gorecore.data.PlayerData$1.writeV(PlayerData.java:33)
at com.crowsofwar.gorecore.util.GoreCoreNBTUtil.writeMapToNBT(GoreCoreNBTUtil.java:161)
at com.crowsofwar.gorecore.data.WorldDataPlayers.func_189551_b(WorldDataPlayers.java:55)
at com.crowsofwar.avatar.common.data.AvatarWorldData.func_189551_b(AvatarWorldData.java:88)
at net.minecraft.world.storage.MapStorage.func_75747_a(SourceFile:92)
at net.minecraft.world.storage.MapStorage.func_75744_a(SourceFile:78)
at net.minecraft.world.WorldServer.func_73042_a(WorldServer.java:1053)
at net.minecraft.world.WorldServer.func_73044_a(WorldServer.java:1001)
at net.minecraft.server.MinecraftServer.func_71267_a(MinecraftServer.java:407)
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:688)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:523)
at java.lang.Thread.run(Unknown Source)

A detailed walkthrough of the error, its code path and all known details is as follows:

-- System Details --
Details:
Minecraft Version: 1.12
Operating System: Windows 10 (x86) version 10.0
Java Version: 1.8.0_251, Oracle Corporation
Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation
Memory: 809259472 bytes (771 MB) / 1037959168 bytes (989 MB) up to 1037959168 bytes (989 MB)
JVM Flags: 2 total; -Xmx1024M -Xms1024M
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
FML: MCP 9.40 Powered by Forge 14.21.1.2387 6 mods loaded, 6 mods active
States: 'U' = Unloaded 'L' = Loaded 'C' = Constructed 'H' = Pre-initialized 'I' = Initialized 'J' = Post-initialized 'A' = Available 'D' = Disabled 'E' = Errored
UCHIJAAAA minecraft{1.12} [Minecraft] (minecraft.jar)
UCHIJAAAA mcp{9.19} [Minecraft Coder Pack] (minecraft.jar)
UCHIJAAAA FML{8.0.99.99} [Forge Mod Loader] (forge-1.12-14.21.1.2387-universal.jar)
UCHIJAAAA forge{14.21.1.2387} [Minecraft Forge] (forge-1.12-14.21.1.2387-universal.jar)
UCHIJAAAA gorecore{1.12.2-0.4.5} [GoreCore] (AVATAR MOD BITCH.jar)
UCHIJAAAA avatarmod{1.5.17-alpha} [Avatar Mod: Out of the Iceberg] (AVATAR MOD BITCH.jar)
Loaded coremods (and transformers):
Profiler Position: N/A (disabled)
Player Count: 2 / 20; [EntityPlayerMP['RairisGamingSK'/41, l='world', x=7644,87, y=84,00, z=5600,44], EntityPlayerMP['PlayazPwnz'/42, l='world', x=7644,25, y=84,00, z=5600,11]]
Is Modded: Definitely; Server brand changed to 'fml,forge'
Type: Dedicated Server (map_server.txt)