Can't query MySQL database?

Question

PHP

Good afternoon, faced such problem. I am using the mysqli_qeury function, but it does not see the variable assigned to the database connection function. The connection to the database itself works, but the request does not go.
Code from dbconect.php

<?php

// Подключение к БД
$myHostName = "localhost";
$myUserName = "root";
$myPassword  = "";
$myDataBase = "";

$dbconnect = mysqli_connect($myHostName,$myUserName,$myPassword,$myDataBase);

// Проверка подключения к БД
if ($dbconnect == true) {
    echo  "<pre>";
    echo "Успешное подключение к БД";
    echo  "<pre>";
}
else{
    echo  "<pre>";
    exit ("Ошибка подключения к БД");
    echo  "<pre>";
    mysqli_close($dbconnect);
}

?>

Code from signup.php

<?php
session_start();
require "dbconect.php";
// Данные регистрации
$first_name = $_POST["first_name"];
$last_name = $_POST["last_name"];
$email = $_POST["email"];
$password = $_POST["password"];
$password_confirm = $_POST["password_confirm"];
$captcha = $_POST["captcha"];

// Проверка паролей и капчи
if (($password == $password_confirm) and ($captcha == $_SESSION["rand"])) {
    header("Location: ../www/form_auto.php");
} else {
    $_SESSION["msg"] = "Пароли не совпадают";
    header("Location: ../www/form_register.php");
}

mysqli_query($dbconnect, INSERT INTO `users` (`id`, `first_name`, `last_name`, `email`, `password`) VALUES (NULL, NULL, NULL, NULL, NULL));

?>

Here is what the console says

Answer 1

Declare the variable as global. Variables in PHP, if I don't confuse anything, are local within the included file.
https://www.php.net/manual/en/language.variables.s...