Hey, how can I add a effect to a Player ?

This is my Code:

<?php

namespace blue;

use pocketmine\plugin\PluginBase;
use pocketmine\Player;
use pocketmine\Server;
use pocketmine\event\Listener;
use pocketmine\event\player\PlayerJoinEvent;
use pocketmine\command\Command;
use pocketmine\command\CommandSender;
use pocketmine\item\Item;
use pocketmine\event\block\BlockPlaceEvent;
use pocketmine\item\enchantment\Enchantment;
use pocketmine\item\enchantment\EnchantmentInstance;
use pocketmine\entity\Effect;
use pocketmine\event\entity\EntityDamageEvent;
use pocketmine\block\Block;
use pocketmine\math\Vector3;
use pocketmine\level\particle\DestroyBlockParticle;
use pocketmine\level\particle\{DustParticle, FlameParticle, FloatingTextParticle, EntityFlameParticle, CriticalParticle, ExplodeParticle, HeartParticle, LavaParticle, MobSpawnParticle, SplashParticle};
use pocketmine\event\player\PlayerMoveEvent;

class Main extends PluginBase implements Listener {

public $plugin;

public function onEnable(){
$this->getLogger()->info("Enable");
$this->getServer()->getPluginManager()->registerEvents($this, $this);
$this->eco = $this->getServer()->getPluginManager()->getPlugin("EconomyAPI");
}

public function onCommand(CommandSender $sender, Command $command, String $label, array $args) : bool {
switch($command->getName()){
case "blue":
$sender->removeAllEffects();
$sender->addEffect(Effect::getEffect(10)->setAmplifier(50)->setDuration(20*2)->setVisible(false));
return true;
}
return true;
}
}

And this is my Problem:

[16:53:50] [Server thread/CRITICAL]: Error: "Call to undefined method pocketmine\entity\Effect::setAmplifier()" (EXCEPTION) in "plugins/blue/src/blue/Main" at line 38

 

I think, I did allthing right, but It don't works

 

I use pmmp Ver. 3.8.3

 

old code, please check the new api

 

I couldn't get it to work either, so I just ran the effect command through the console.