获取连接失败：php_network_getaddresses：getaddrinfo failed：

<?php

$servername = "http://www.url.com";
$username = "db_username";
$password = "db_password";
$databaseName = "db_name";

$connect = new mysqli($servername,$username,$password,$databaseName);

if ($connect->connect_error) {
    die("Connection failed: " . $connect->connect_error);
} 
echo "Connected successfully";

?>

这是insert.php文件,也存储在http://www.url.com/public_html中,用于在数据库中插入数据.

<?php

if($_SERVER["REQUEST_METHOD"]=="POST"){
    require'connection.php';
    createStudent();
}
function createStudent(){

    global $connect;

    $name = $_POST["name"];
    $lastname = $_POST["lastname"];
    $age = $_POST["age"];

    $query="INSERT INTO  `demo` (  `name`,`lastname`,`age` ) 
    VALUES ('$name','$lastname','$age')";
    mysqli_query($connect,$query)or die (mysqli_error($connect));
    mysqli_close($connect);
}
?>

我使用邮递员和我的Android应用程序来测试这个,但我得到：
连接失败：php_network_getaddresses：getaddrinfo failed：名称或服务未知错误.

我不是一个PHP开发人员,但我看不到我的PHP文件中的任何错误,所以任何帮助将受到欢迎.

提前致谢.