PayPal\Api\Payee::setMerchantId PHP Method

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

 public static function createPayee()
 {
     $payee = new Payee();
     $payee->setEmail(self::$email);
     $payee->setMerchantId(self::$merchant_id);
     $payee->setPhone(self::$phone);
     return $payee;
 }