Scoreboard Plugin (Scoreboard Doesn't Show up)

I've been developing a plugin that I can use just simply for a player to type a command like /adventurer then it would give them some certain items, but the problem i'm having is when the player joins or even types /adventurer the scoreboard wont show up. I've done lots of searching for help on this but I cant seem to be able to solve it still. (I have never made a scoreboard plugin so sorry if its like a noob mistake)

Code:

package me.RektSoul.MCClasses;

import org.bukkit.Bukkit;
import org.bukkit.ChatColor;
import org.bukkit.Material;
import org.bukkit.Sound;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.player.PlayerJoinEvent;
import org.bukkit.inventory.ItemStack;
import org.bukkit.plugin.java.JavaPlugin;
import org.bukkit.scoreboard.DisplaySlot;
import org.bukkit.scoreboard.Objective;
import org.bukkit.scoreboard.Scoreboard;
import org.bukkit.scoreboard.ScoreboardManager;
import org.bukkit.scoreboard.Team;

public class MCClasses extends JavaPlugin implements Listener {
   
    ScoreboardManager manager = Bukkit.getScoreboardManager();
    Scoreboard board = manager.getNewScoreboard();
   
    // Classes //
    Team adven = board.registerNewTeam(DisplaySlot.SIDEBAR + "adventurer");
    Team arch = board.registerNewTeam(DisplaySlot.SIDEBAR + "Archer");
   
    Objective objective = board.registerNewObjective("test", "dummy");
   
    @Override
    public void onEnable() {
      Bukkit.getServer().getPluginManager().registerEvents(this, this);
    }

    @SuppressWarnings("deprecation")
    @EventHandler
    public void onJoin(PlayerJoinEvent event){
        Player player = event.getPlayer();
        adven.addPlayer(player);
        player.setScoreboard(board);
        objective.setDisplaySlot(DisplaySlot.SIDEBAR);
    }
   
    @SuppressWarnings("deprecation")
    public boolean onCommand(CommandSender sender, Command cmd, String label, String[]args) {
       
        if(cmd.getName().equalsIgnoreCase("TestMCC") && sender instanceof Player) {
           
            Player player = (Player) sender;
       
              player.sendMessage(ChatColor.GREEN + "MC Classes is working " + ChatColor.BOLD + player.getName());
               player.playSound(player.getLocation(), Sound.ENTITY_FIREWORK_BLAST, 1, 1);  
               {
        }
        }
       
        // Items //
        ItemStack Lchest = new ItemStack (Material.LEATHER_CHESTPLATE);
       
        // Commands //
               if(cmd.getName().equalsIgnoreCase("Adventurer") && sender instanceof Player) {
                 
                  Player player = (Player) sender;
                 
                  player.playSound(player.getLocation(), Sound.ENTITY_PLAYER_BURP, 1, 1);
                  player.sendMessage(ChatColor.DARK_PURPLE + "Your are now an adventurer");
                  player.setItemInHand(Lchest);
                  player.setCustomNameVisible(true);
                 
            return true;
           
        }
        return false;
  }
}

 

@ibareis
Have you tried setting the player's scoreboard after you add the player to the scoreboard? Also, things like the displayname and the displayslot should be set only once, at it should be set before the players are added.

 

I changed it up a bit, but im Still Having Issues (sorry if i didn't use the information you gave correctly)