Help me fix it

Could not pass event 'pocketmine\event\server\DataPacketReceiveEvent' to 'FormAPI v1.0.0': Call to a member function myMoney() on null on jojoe77777\FormAPI\FormAPI
Error: "Call to a member function myMoney() on null" (EXCEPTION) in "plugins/EnchantUI_raw/src/ID/armor/antiknockback" at line 25

PHP:

<?php

namespace ID\armor;

use pocketmine\Player;
use pocketmine\command\ConsoleCommandSender;
use pocketmine\utils\TextFormat;
use pocketmine\item\Armor;
use EnchantUI\Main;
// EconomyAPI
use onebone\economyapi\EconomyAPI;

class antiknockback{

public $eco;
    private $plugin;

    public function __construct(Main $plugin){
        $this->plugin = $plugin;
    }
    
    public function init(Player $sender){
        $eco = $this->plugin->getServer()->getPluginManager()->getPlugin("EconomyAPI");
        $api = $this->plugin->getServer()->getPluginManager()->getPlugin("FormAPI");
        $money = $this->eco->myMoney($sender->getName());
        $form = $api->createCustomForm(function (Player $sender, array $data){
            $result = $data[0];
            $player = $sender->getName();
       $item = $sender->getInventory()->getItemInHand();
            if($result != null){
                if ($item instanceof Armor) {
                                    if($money >= 5000){
                                       $this->eco->grantMoney($sender->getName(),-5000);
                        $this->plugin->getServer()->dispatchCommand(new ConsoleCommandSender, "ce enchant antiknockback $result $player");
                      $sender->sendMessage(" $data[1] Enchant thành công!");
                                      return true;
                                    }else{
                                       $sender->sendMessage("no money");
                                    }
        
        return true;
            }else{
                $sender->sendMessage("Enchant này chỉ có hiệu quả với Giáp");
            }
            }
        });
        $form->setTitle(TextFormat::BLUE . "--= " . TextFormat::RED . "EnchantUI" . TextFormat::BLUE . " =--");
        $form->addSlider("Max Level:", 1, 1, -1, -1); #rare
        $form->addLabel("Giảm lượt knockdown xuống 25% cho mỗi bộ giáp");
        ;$form->sendToPlayer($sender);
    }
    }

 

It happens because you are trying to access a class variable which is currently set to null. Replace

PHP:

$this->eco->myMoney($sender->getName());

with

PHP:

$eco->myMoney($sender->getName());

They are not the same. With $this->variable you access to a class variable while with $variable you access to a function variable (local).
In your case you set the EconomyAPI instance into the function's variable $eco and you left the class variable "$this->eco" null.
Keep also in mind that to pass variables inside closures you must specify them with the use construct.
In essence you should replace:

PHP:

function (Player $sender, array $data){

with

PHP:

function (Player $sender, array $data) use ($money){

Also be careful when you use $this variable inside closures.

 

thank you and
For this part I have to do "$this->eco->reduceMoney($sender->getName(),-5000);"