Fabric is a terrible modding platform.

common/src/main/java/ru/octol1ttle/knockdowns/common/KnockdownsClient.java

@@ -0,0 +1,19 @@
+package ru.octol1ttle.knockdowns.common;
+
+import net.minecraft.client.MinecraftClient;
+import net.minecraft.util.math.Vec3d;
+import ru.octol1ttle.knockdowns.common.events.KnockdownsClientEvents;
+import ru.octol1ttle.knockdowns.common.registries.KnockdownsSoundEvents;
+import ru.octol1ttle.knockdowns.common.registries.KnockedDownSoundInstance;
+
+public class KnockdownsClient {
+    public static void init() {
+        KnockdownsClientEvents.registerCallbacks();
+    }
+
+    public static void playKnockedDownSound(Vec3d pos) {
+        MinecraftClient.getInstance().getSoundManager().play(
+                new KnockedDownSoundInstance(KnockdownsSoundEvents.KNOCKED_DOWN.get(), pos)
+        );
+    }
+}

common/src/main/java/ru/octol1ttle/knockdowns/common/KnockdownsCommon.java

@@ -1,7 +1,7 @@
 package ru.octol1ttle.knockdowns.common;
 
-import ru.octol1ttle.knockdowns.common.events.KnockdownsClientEvents;
 import ru.octol1ttle.knockdowns.common.events.KnockdownsEvents;
+import ru.octol1ttle.knockdowns.common.network.KnockdownsNetwork;
 import ru.octol1ttle.knockdowns.common.registries.KnockdownsSoundEvents;
 
 public class KnockdownsCommon {
@@ -10,7 +10,6 @@ public class KnockdownsCommon {
     public static void init() {
         KnockdownsSoundEvents.register();
         KnockdownsNetwork.registerPackets();
-        KnockdownsClientEvents.registerCallbacks();
         KnockdownsEvents.registerCallbacks();
     }
 }

common/src/main/java/ru/octol1ttle/knockdowns/common/events/KnockdownsClientEvents.java

@@ -11,10 +11,10 @@ import net.minecraft.client.MinecraftClient;
 import net.minecraft.client.font.TextRenderer;
 import net.minecraft.util.hit.EntityHitResult;
 import net.minecraft.util.hit.HitResult;
-import ru.octol1ttle.knockdowns.common.KnockdownsNetwork;
+import ru.octol1ttle.knockdowns.common.network.KnockdownsNetwork;
 import ru.octol1ttle.knockdowns.common.api.IKnockableDown;
-import ru.octol1ttle.knockdowns.common.packets.KnockedDownStatusPacket;
+import ru.octol1ttle.knockdowns.common.network.packets.KnockedDownStatusPacket;
-import ru.octol1ttle.knockdowns.common.packets.ReviveStatusPacket;
+import ru.octol1ttle.knockdowns.common.network.packets.ReviveStatusPacket;
 
 public class KnockdownsClientEvents {
     private static final int REVIVAL_WAIT_TIME = 10 * SharedConstants.TICKS_PER_SECOND;
@@ -22,13 +22,13 @@ public class KnockdownsClientEvents {
     private static int revivalTimer = -1;
 
     public static void registerCallbacks() {
-        registerOnEntityLoad();
+        registerOnClientPlayerJoin();
         registerOnEntityUse();
         registerOnWorldTick();
         registerOnHudRender();
     }
 
-    private static void registerOnEntityLoad() {
+    private static void registerOnClientPlayerJoin() {
         ClientPlayerEvent.CLIENT_PLAYER_JOIN.register(player -> {
             UUID playerUuid = player.getUuid();
             KnockdownsNetwork.sendToServer(new KnockedDownStatusPacket.RequestC2S(playerUuid));
@@ -38,7 +38,7 @@ public class KnockdownsClientEvents {
 
     private static void registerOnEntityUse() {
         InteractionEvent.INTERACT_ENTITY.register((player, entity, hand) -> {
-            if (!(entity instanceof IKnockableDown knockableEntity) || !knockableEntity.knockdowns$isKnockedDown()
+            if (!player.getWorld().isClient() || !(entity instanceof IKnockableDown knockableEntity) || !knockableEntity.knockdowns$isKnockedDown()
                     || knockableEntity.knockdowns$isBeingRevived()) {
                 return EventResult.pass();
             }

common/src/main/java/ru/octol1ttle/knockdowns/common/events/KnockdownsEvents.java

@@ -11,10 +11,10 @@ import net.minecraft.text.Text;
 import net.minecraft.text.TranslatableTextContent;
 import net.minecraft.util.Hand;
 import net.minecraft.world.GameRules;
-import ru.octol1ttle.knockdowns.common.KnockdownsNetwork;
+import ru.octol1ttle.knockdowns.common.network.KnockdownsNetwork;
 import ru.octol1ttle.knockdowns.common.api.IKnockableDown;
-import ru.octol1ttle.knockdowns.common.packets.KnockedDownStatusPacket;
+import ru.octol1ttle.knockdowns.common.network.packets.KnockedDownStatusPacket;
-import ru.octol1ttle.knockdowns.common.packets.PlayKnockedDownSoundS2CPacket;
+import ru.octol1ttle.knockdowns.common.network.packets.PlayKnockedDownSoundS2CPacket;
 
 public class KnockdownsEvents {
     public static void registerCallbacks() {

common/src/main/java/ru/octol1ttle/knockdowns/common/mixin/PlayerEntityMixin.java

@@ -15,9 +15,9 @@ import ru.octol1ttle.knockdowns.common.api.IKnockableDown;
 @Mixin(PlayerEntity.class)
 public abstract class PlayerEntityMixin implements IKnockableDown {
     @Unique
-    private boolean knockedDown;
+    private boolean knockdowns$knockedDown;
     @Unique
-    private boolean beingRevived;
+    private boolean knockdowns$beingRevived;
 
     @ModifyExpressionValue(method = "updatePose", at = @At(value = "INVOKE", target = "Lnet/minecraft/entity/player/PlayerEntity;isSwimming()Z"))
     private boolean enterSwimmingIfKnockedDown(boolean original) {
@@ -36,32 +36,32 @@ public abstract class PlayerEntityMixin implements IKnockableDown {
 
     @Inject(method = "readCustomDataFromNbt", at = @At("TAIL"))
     public void readKnockedDownFromNbt(NbtCompound nbt, CallbackInfo ci) {
-        this.knockedDown = nbt.getBoolean("KnockedDown");
+        this.knockdowns$knockedDown = nbt.getBoolean("KnockedDown");
     }
 
     @Inject(method = "writeCustomDataToNbt", at = @At("TAIL"))
     public void writeKnockedDownToNbt(NbtCompound nbt, CallbackInfo ci) {
-        nbt.putBoolean("KnockedDown", this.knockedDown);
+        nbt.putBoolean("KnockedDown", this.knockdowns$knockedDown);
     }
 
     @Override
     public boolean knockdowns$isKnockedDown() {
-        return knockedDown;
+        return knockdowns$knockedDown;
     }
 
     @Override
     public void knockdowns$setKnockedDown(boolean knockedDown) {
-        this.knockedDown = knockedDown;
+        this.knockdowns$knockedDown = knockedDown;
     }
 
     @Override
     public boolean knockdowns$isBeingRevived() {
-        return beingRevived;
+        return knockdowns$beingRevived;
     }
 
     @Override
     public void knockdowns$setBeingRevived(boolean beingRevived) {
-        this.beingRevived = beingRevived;
+        this.knockdowns$beingRevived = beingRevived;
     }
 
     @Override

common/src/main/java/ru/octol1ttle/knockdowns/common/network/KnockdownsNetwork.java

@@ -1,4 +1,4 @@
-package ru.octol1ttle.knockdowns.common;
+package ru.octol1ttle.knockdowns.common.network;
 
 import dev.architectury.networking.NetworkChannel;
 import dev.architectury.networking.NetworkManager;
@@ -11,9 +11,10 @@ import net.minecraft.server.world.ServerChunkManager;
 import net.minecraft.server.world.ServerWorld;
 import net.minecraft.server.world.ThreadedAnvilChunkStorage;
 import net.minecraft.util.Identifier;
-import ru.octol1ttle.knockdowns.common.packets.KnockedDownStatusPacket;
+import ru.octol1ttle.knockdowns.common.KnockdownsCommon;
-import ru.octol1ttle.knockdowns.common.packets.PlayKnockedDownSoundS2CPacket;
+import ru.octol1ttle.knockdowns.common.network.packets.KnockedDownStatusPacket;
-import ru.octol1ttle.knockdowns.common.packets.ReviveStatusPacket;
+import ru.octol1ttle.knockdowns.common.network.packets.PlayKnockedDownSoundS2CPacket;
+import ru.octol1ttle.knockdowns.common.network.packets.ReviveStatusPacket;
 
 public class KnockdownsNetwork {
     private static final NetworkChannel CHANNEL = NetworkChannel.create(new Identifier(KnockdownsCommon.MOD_ID, "main"));

common/src/main/java/ru/octol1ttle/knockdowns/common/network/packets/KnockdownsPacket.java

@@ -1,14 +1,10 @@
-package ru.octol1ttle.knockdowns.common.packets;
+package ru.octol1ttle.knockdowns.common.network.packets;
 
 import dev.architectury.networking.NetworkManager;
 import java.util.function.Supplier;
 import net.minecraft.network.PacketByteBuf;
 
 public abstract class KnockdownsPacket {
-    public KnockdownsPacket(PacketByteBuf buf) {
-        // Decode data into a message
-    }
-
     public KnockdownsPacket(/* args here */) {
         // Message creation
     }

common/src/main/java/ru/octol1ttle/knockdowns/common/network/packets/KnockedDownStatusPacket.java

@@ -1,10 +1,10 @@
-package ru.octol1ttle.knockdowns.common.packets;
+package ru.octol1ttle.knockdowns.common.network.packets;
 
 import dev.architectury.networking.NetworkManager;
 import java.util.UUID;
 import java.util.function.Supplier;
 import net.minecraft.network.PacketByteBuf;
-import ru.octol1ttle.knockdowns.common.KnockdownsNetwork;
+import ru.octol1ttle.knockdowns.common.network.KnockdownsNetwork;
 import ru.octol1ttle.knockdowns.common.api.IKnockableDown;
 
 public class KnockedDownStatusPacket {

common/src/main/java/ru/octol1ttle/knockdowns/common/network/packets/PlayKnockedDownSoundS2CPacket.java

@@ -1,12 +1,10 @@
-package ru.octol1ttle.knockdowns.common.packets;
+package ru.octol1ttle.knockdowns.common.network.packets;
 
 import dev.architectury.networking.NetworkManager;
 import java.util.function.Supplier;
-import net.minecraft.client.MinecraftClient;
 import net.minecraft.network.PacketByteBuf;
 import net.minecraft.util.math.Vec3d;
-import ru.octol1ttle.knockdowns.common.registries.KnockdownsSoundEvents;
+import ru.octol1ttle.knockdowns.common.KnockdownsClient;
-import ru.octol1ttle.knockdowns.common.registries.KnockedDownSoundInstance;
 
 public class PlayKnockedDownSoundS2CPacket extends KnockdownsPacket {
     private final double x;
@@ -33,8 +31,6 @@ public class PlayKnockedDownSoundS2CPacket extends KnockdownsPacket {
     @Override
     public void apply(Supplier<NetworkManager.PacketContext> contextSupplier) {
         NetworkManager.PacketContext context = contextSupplier.get();
-        context.queue(() -> MinecraftClient.getInstance().getSoundManager().play(
+        context.queue(() -> KnockdownsClient.playKnockedDownSound(new Vec3d(this.x, this.y, this.z)));
-                new KnockedDownSoundInstance(KnockdownsSoundEvents.KNOCKED_DOWN.get(), new Vec3d(this.x, this.y, this.z))
-        ));
     }
 }

common/src/main/java/ru/octol1ttle/knockdowns/common/network/packets/ReviveStatusPacket.java

@@ -1,11 +1,11 @@
-package ru.octol1ttle.knockdowns.common.packets;
+package ru.octol1ttle.knockdowns.common.network.packets;
 
 import dev.architectury.networking.NetworkManager;
 import java.util.UUID;
 import java.util.function.Supplier;
 import net.minecraft.entity.player.PlayerEntity;
 import net.minecraft.network.PacketByteBuf;
-import ru.octol1ttle.knockdowns.common.KnockdownsNetwork;
+import ru.octol1ttle.knockdowns.common.network.KnockdownsNetwork;
 import ru.octol1ttle.knockdowns.common.api.IKnockableDown;
 
 public class ReviveStatusPacket {

fabric/src/main/java/ru/octol1ttle/knockdowns/fabric/KnockdownsFabricClient.java

@@ -0,0 +1,11 @@
+package ru.octol1ttle.knockdowns.fabric;
+
+import net.fabricmc.api.ClientModInitializer;
+import ru.octol1ttle.knockdowns.common.KnockdownsClient;
+
+public class KnockdownsFabricClient implements ClientModInitializer {
+    @Override
+    public void onInitializeClient() {
+        KnockdownsClient.init();
+    }
+}

fabric/src/main/resources/fabric.mod.json

@@ -17,6 +17,9 @@
   "entrypoints": {
     "main": [
       "ru.octol1ttle.knockdowns.fabric.KnockdownsFabric"
+    ],
+    "client": [
+      "ru.octol1ttle.knockdowns.fabric.KnockdownsFabricClient"
     ]
   },
   "mixins": [

forge/src/main/java/ru/octol1ttle/knockdowns/forge/KnockdownsForge.java

@@ -1,10 +1,14 @@
 package ru.octol1ttle.knockdowns.forge;
 
 import dev.architectury.platform.forge.EventBuses;
+import net.minecraftforge.eventbus.api.SubscribeEvent;
 import net.minecraftforge.fml.common.Mod;
+import net.minecraftforge.fml.event.lifecycle.FMLClientSetupEvent;
 import net.minecraftforge.fml.javafmlmod.FMLJavaModLoadingContext;
+import ru.octol1ttle.knockdowns.common.KnockdownsClient;
 import ru.octol1ttle.knockdowns.common.KnockdownsCommon;
 
+@SuppressWarnings("unused")
 @Mod(KnockdownsCommon.MOD_ID)
 public class KnockdownsForge {
     public KnockdownsForge() {
@@ -12,4 +16,9 @@ public class KnockdownsForge {
         EventBuses.registerModEventBus(KnockdownsCommon.MOD_ID, FMLJavaModLoadingContext.get().getModEventBus());
         KnockdownsCommon.init();
     }
+
+    @SubscribeEvent
+    public void onInitializeClient(FMLClientSetupEvent event) {
+        KnockdownsClient.init();
+    }
 }