PayU\Configuration::setMerchantId PHP Method

    public function setMerchantId($merchantId)
    {
        $this->merchantId = $merchantId;
        return $this;
    }

 public function setUp()
 {
     $configuration = new Configuration();
     $configuration->setMerchantId('MY_MERCHANT_01')->setSecretKey('SECRET_KEY')->setPaymentEndpointUrl('https://secure.payu.com.tr/order/alu/v3')->setLoyaltyInquiryEndPointUrl('https://secure.payu.com.tr/api/loyalty-points/check');
     $this->configuration = $configuration;
     $this->client = new Client($configuration);
 }