Не добавляется информация в бд

<?php
require ('app_config.php');
$link = mysqli_connect(DATABASE_HOST,DATABASE_USERNAME,DATABASE_PASSWORD,DATABASE_NAME) or die(connect_error());
?>

require ('../db_config/connect.php');
$first_name = $_POST['first_name'];
$last_name = $_POST['last_name'];
$email = $_POST['email'];
$facebook = $_POST['facebook_url'];
$twitter = $_POST['twitter_handle'];
$bio = $_POST['bio'];
 
$request = "insert into users (first_name,last_name,email,facebook,twitter,bio) values ('{$first_name}','{$last_name}','{$email}','{$facebook}','{$twitter}','{$twitter}','{$bio}');";
$result = mysqli_query($link,$request);

$request = "insert into users (first_name,last_name,email,facebook,twitter,bio) values ('$first_name', '$last_name', '$email', '$facebook', '$twitter', '$twitter', '$bio')";

$result = mysqli_query($link,$request) or die(mysqli_error());

$result = mysqli_query($link,$request);
if (!$result)
{
    mysqli_error();
}

$request = "insert into users (first_name,last_name,email,facebook,twitter,bio) values ('{$first_name}','{$last_name}','{$email}','{$facebook}','{$twitter}','{$twitter}','{$bio}');";

(first_name,last_name,email,facebook,twitter,bio)

('{$first_name}','{$last_name}','{$email}','{$facebook}','{$twitter}','{$twitter}','{$bio}')

{$bio}');";

{$bio}')";