1.19.2 sending packet from server to client problem

[Westlifers]

Hi, I'm new to modding, and I'm trying to validate wether a string is in a list. However, the list is in ServerLevel's capability and I can't validata it directly on client.

Later I came up with this idea: whenever I need this list, I may send a packet from client to sever, and inside the handler I send another packet to client, which synchronize the list to client. (I came up with this while watching this vedio: 

 

The problem is: packet from client to server works perfectly(I've done this several times before so I got some experience) BUT packet from server to client doesn't work. 

Packet from client to server: 

public class RequestSyncLevelDataS2CPacket {

    public RequestSyncLevelDataS2CPacket() {

    }

    public RequestSyncLevelDataS2CPacket(FriendlyByteBuf buf) {

    }

    public void toBytes(FriendlyByteBuf buf) {

    }

    public void handle(Supplier<NetworkEvent.Context> ctx) {
        ctx.get().enqueueWork(() -> {
            System.out.println("sent");
            ModMessages.sendToPlayer(new SyncLevelDataS2CPacket(), ctx.get().getSender());
        });
    }
}

Packet from server to client:

public class SyncLevelDataS2CPacket {

    public SyncLevelDataS2CPacket() {

    }

    public SyncLevelDataS2CPacket(FriendlyByteBuf buf) {

    }

    public void toBytes(FriendlyByteBuf buf) {

    }

    public boolean handle(Supplier<NetworkEvent.Context> ctx) {
        ctx.get().enqueueWork(() -> {
            ServerLevel level = ctx.get().getSender().getLevel();
            System.out.println("hiiiiiiiiiii");
            level.getCapability(LevelCapabilityProvider.LEVEL_CAPABILITY).ifPresent(cap -> {
                System.out.println("set");
                ClientLevelData.setMap(cap.getClassMap());
            });
        });
        ctx.get().setPacketHandled(true);
        return true;
    }
}

AND below is my ClientLevelData, where I store the map(this map has the list I want)

public class ClientLevelData {
    private static Map<String, List<String>> map;

    public static void setMap(Map<String, List<String>> map) {
        ClientLevelData.map = map;
    }

    public static Map<String, List<String>> getMap() {
        return map;
    }
}

I do registered these packets like this:

net.messageBuilder(SyncLevelDataS2CPacket.class, id(), NetworkDirection.PLAY_TO_CLIENT)
                .decoder(SyncLevelDataS2CPacket::new)
                .encoder(SyncLevelDataS2CPacket::toBytes)
                .consumerMainThread(SyncLevelDataS2CPacket::handle)
                .add();

net.messageBuilder(RequestSyncLevelDataS2CPacket.class, id(), NetworkDirection.PLAY_TO_SERVER)
                .decoder(RequestSyncLevelDataS2CPacket::new)
                .encoder(RequestSyncLevelDataS2CPacket::toBytes)
                .consumerMainThread(RequestSyncLevelDataS2CPacket::handle)
                .add();

other packets all work perfectly. and I tried not using RequestSyncLevelDataS2CPacket, and found that whatever way of sending SyncLevelDataS2CPacket will fail. I get no print from it. I'm really confused.

[Westlifers]

ADD:

I found that this packet is actually sent but ctx.get().enqueueWork didn't work. The program stucks there: 
 

    public boolean handle(Supplier<NetworkEvent.Context> ctx) {
        System.out.println("h232323");
        ctx.get().enqueueWork(() -> {
            ServerLevel level = Objects.requireNonNull(ctx.get().getSender()).getLevel();
            System.out.println("hiiiiiiiiiii");
            level.getCapability(LevelCapabilityProvider.LEVEL_CAPABILITY).ifPresent(cap -> {
                System.out.println("set");
                ClientLevelData.setMap(cap.getClassMap());
            });
        });
        System.out.println("11111");
        ctx.get().setPacketHandled(true);
        return true;
    }

will only print "h232323".