hum... my code dont work

this is my code ::

PHP:

<?php

namespace oi;

use pocketmine\Player;
use pocketmine\plugin\PluginBase;
use pocketmine\entity\Effect;
use pocketmine\level\particle\PortalParticle;
use pocketmine\command\CommandSender;
use pocketmine\event\Listener;
use pocketmine\utils\TextFormat as Color;
use pocketmine\command\Command;
use pocketmine\math\Vector3;
use pocketmine\item\Item;

class main extends PluginBase implements Listener {
   
    public function onEnable() {
        $this->getLogger()->info(Color::GREEN."on!");
    }
   
    public function onCommand(CommandSender $sender,Command $cmd,$label,array $args) {
            if($sender instanceof Player) {
            if((strtolower($cmd->getName()) == "oi") && isset($args[0])) {
            $player = $this->getServer()->getPlayer($args[0]);
            if($player instanceof Player){
            $level = $player->getLevel();
            $level->setBlock(new Vector3($player->x, $player->y, $player->z),Block::get(42,0));
            $level->setBlock(new Vector3($player->x, $player->y + 1, $player->z),Block::get(42,0));
            $player->addEffect(Effect::getEffect(9)->setDuration(100)->setAmplifier(9));
            $level->addParticle(new PortalParticle(new Vector3($player->x, $player->y, $player->z)));
            } else { $sender->sendMessage("Player not found"); }
            }
        }
    }
}

the error ::
"An unknown error occurred while attempting to perform this command"
and thankis

Well... what does the error say in the console

extra (