import io.netty.buffer.ByteBuf;
import net.minecraft.client.Minecraft;
import net.minecraftforge.fml.common.Mod;
import net.minecraftforge.fml.common.event.FMLInitializationEvent;
import net.minecraftforge.fml.common.eventhandler.SubscribeEvent;
import net.minecraftforge.fml.common.network.FMLEventChannel;
import net.minecraftforge.fml.common.network.FMLNetworkEvent;
import net.minecraftforge.fml.common.network.NetworkRegistry;

import java.io.ByteArrayInputStream;
import java.io.DataInputStream;

@Mod(modid = "meinmod", name = "MeinMod", version = "1.0")
public class MeinMod {

   private static final String CHANNEL = "griefergames:main";

   @Mod.EventHandler
   public void init(FMLInitializationEvent event) {
      // Kanal registrieren und diese Klasse als Listener anmelden
      FMLEventChannel channel = NetworkRegistry.INSTANCE.newEventDrivenChannel(CHANNEL);
      channel.register(this);
   }

   @SubscribeEvent
   public void onCustomPacket(FMLNetworkEvent.ClientCustomPacketEvent event) {
      ByteBuf buf = event.getPacket().payload();
      byte[] data = new byte[buf.readableBytes()];
      buf.readBytes(data);

      try (DataInputStream in = new DataInputStream(new ByteArrayInputStream(data))) {
         String id = in.readUTF();

         switch (id) {
            case "accountbalance": {
               double balance = in.readDouble();
               Minecraft.getMinecraft().addScheduledTask(() -> onMoneyUpdate(balance));
               break;
            }

            case "bankbalance": {
               double balance = in.readDouble();
               Minecraft.getMinecraft().addScheduledTask(() -> onBankUpdate(balance));
               break;
            }

            case "blockoftheday": {
               String type = in.readUTF();
               String blockMaterial = in.readUTF();
               int blockData = in.readInt();
               String entityType = in.readUTF();
               
               // type ist "BLOCK"/"MATERIAL" → blockMaterial gefüllt, entityType leer
               // type ist "ENTITY" → entityType gefüllt, blockMaterial leer
               Minecraft.getMinecraft().addScheduledTask(() -> onBlockOfTheDay(type, blockMaterial, blockData, entityType));
               break;
            }

            case "blockoftheday_progress": {
               Minecraft.getMinecraft().addScheduledTask(() -> onBlockProgressUpdate());
               break;
            }

            case "booster": {
               int count = in.readInt();
               for (int i = 0; i < count; i++) {
                  String type = in.readUTF();
                  int multiplier = in.readInt();
                  int tierCount = in.readInt();
                  long[] remainingSecondsPerTier = new long[tierCount];
                  for (int t = 0; t < tierCount; t++) {
                     remainingSecondsPerTier[t] = in.readLong();
                  }
                  Minecraft.getMinecraft().addScheduledTask(() -> onBooster(type, multiplier, remainingSecondsPerTier));
               }
               break;
            }

            case "clearlag": {
               long remainingSeconds = in.readLong();
               Minecraft.getMinecraft().addScheduledTask(() -> onClearLag(remainingSeconds));
               break;
            }

            case "entityremover": {
               long remainingSeconds = in.readLong();
               Minecraft.getMinecraft().addScheduledTask(() -> onEntityRemover(remainingSeconds));
               break;
            }

            case "plotchat_configuration": {
               boolean status = in.readBoolean();
               Minecraft.getMinecraft().addScheduledTask(() -> onPlotChatConfig(status));
               break;
            }

            default:
               // Unbekannte ID ignorieren
               // Neue Payloads können jederzeit hinzukommen
               break;
         }

      } catch (Exception e) {
         e.printStackTrace();
      }
   }
}

import net.labymod.api.client.component.event.PluginMessageEvent;
import net.labymod.api.event.Subscribe;

import java.io.DataInputStream;
import java.io.ByteArrayInputStream;

public class MeinPayloadListener {

    @Subscribe
    public void onPluginMessage(PluginMessageEvent event) {
        if (!"griefergames:main".equals(event.getIdentifier())) return;

        byte[] data = event.getData();
        try (DataInputStream in = new DataInputStream(new ByteArrayInputStream(data))) {
            String id = in.readUTF();

            switch (id) {
                case "accountbalance": {
                    double balance = in.readDouble();
                    MeinAddon.onMoneyUpdate(balance);
                    break;
                }

                case "bankbalance": {
                    double balance = in.readDouble();
                    MeinAddon.onBankUpdate(balance);
                    break;
                }

                case "blockoftheday": {
                    String type = in.readUTF();
                    String blockMaterial = in.readUTF();
                    int blockData = in.readInt();
                    String entityType = in.readUTF();
                    
                    // type ist "BLOCK"/"MATERIAL" → blockMaterial gefüllt, entityType leer
                    // type ist "ENTITY" → entityType gefüllt, blockMaterial leer
                    MeinAddon.onBlockOfTheDay(type, blockMaterial, blockData, entityType);
                    break;
                }

                case "blockoftheday_progress": {
                    MeinAddon.onBlockProgressUpdate();
                    break;
                }

                case "booster": {
                    int count = in.readInt();
                    for (int i = 0; i < count; i++) {
                        String type = in.readUTF();
                        int multiplier = in.readInt();
                        int tierCount = in.readInt();
                        long[] remainingSecondsPerTier = new long[tierCount];
                        for (int t = 0; t < tierCount; t++) {
                            remainingSecondsPerTier[t] = in.readLong();
                        }
                        MeinAddon.onBooster(type, multiplier, remainingSecondsPerTier);
                    }
                    break;
                }

                case "clearlag": {
                    long remainingSeconds = in.readLong();
                    MeinAddon.onClearLag(remainingSeconds);
                    break;
                }

                case "entityremover": {
                    long remainingSeconds = in.readLong();
                    MeinAddon.onEntityRemover(remainingSeconds);
                    break;
                }

                case "plotchat_configuration": {
                    boolean status = in.readBoolean();
                    MeinAddon.onPlotChatConfig(status);
                    break;
                }

                default:
                    // Unbekannte ID ignorieren
                    // Neue Payloads können jederzeit hinzukommen
                    break;
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Den Listener im AddonEntryPoint registrieren:

labyAPI().eventBus().registerListener(new MeinPayloadListener());

Das Payload kommt als clientbound Plugin Message-Packet auf dem Channel griefergames:main an. Den Datenbereich mit einem DataInputStream lesen, wie in den Beispielen oben gezeigt.