1.15.2 What am i doing wrong here? (SOLVED)

Code (Java):

package xFadedxShadow.Essentials.Commands;

import java.util.HashSet;
import java.util.Set;
import java.util.UUID;

import org.bukkit.command.Command;
import org.bukkit.command.CommandExecutor;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.entity.EntityDamageEvent;
import org.bukkit.event.entity.EntityDamageEvent.DamageCause;

import xFadedxShadow.Essentials.Main;
import xFadedxShadow.Essentials.Utils.Utils;

public class FlyCommand implements CommandExecutor, Listener {

    private Main plugin;
    private Set<UUID> hadFlight;

    public FlyCommand(Main plugin) {
        this.plugin = plugin;
        hadFlight = new HashSet<>();
        plugin.getCommand("fly").setExecutor(this);
    }

    @Override
    public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {
        if (!(sender instanceof Player)) {
            sender.sendMessage(Utils.chat(plugin.getConfig().getString("permission_error_message")));
            return true;
        }

        Player p = (Player) sender;

        if (p.hasPermission("faded-essentials.fly")) {
            if (!p.getAllowFlight()) {
                hadFlight.add(p.getUniqueId());
                p.setAllowFlight(true);
                p.sendMessage(Utils.chat(plugin.getConfig().getString("FlyCommand.flying_enabled_message")));
                return true;
            } else {
                p.setFlying(false);
                p.setAllowFlight(false);
                p.sendMessage(Utils.chat(plugin.getConfig().getString("FlyCommand.flying_disabled_message")));
                return true;
            }
        } else {
            p.sendMessage(Utils.chat(plugin.getConfig().getString("permission_error_message")));
        }

        return false;

    }
   
    @EventHandler
    public void onFallDamage(EntityDamageEvent e) {
        if (e.getEntity() instanceof Player) {
            Player p = (Player) e.getEntity();
            if (e.getCause() == DamageCause.FALL) {
                if (hadFlight.contains(p.getUniqueId())) {
                    e.setCancelled(true);
                    hadFlight.remove(p.getUniqueId());
                }
            }
        }
   
    }

}