PHP MySQL不能写在表上

While the request completes without an error it doesn't write in the database. It connects to the database i've checked it.

This is my code:

<?php
$json = json_decode(file_get_contents("config.json"), true);
$dbuser = $json['dbuser'];
$servername = $json['dbip'];
$dbpass = $json['dbpass'];
$dbname = $json['dbname'];
$password = $_GET['password'];
$email = $_GET['email'];

// Create connection
$conn = mysqli_connect($servername, $dbuser, $dbpass);
mysql_select_db( $dbname );

// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
} 

$sql = "INSERT INTO credentials (usermail, pass)
VALUES ($email, $password)";

?>

Example: http://localhost/php/database.php?email=random@mail.com&password=ilovestackoverflow

It just doesn't do anything. Please if you have any ideas

you must quote strings like:

$sql = "INSERT INTO credentials (usermail, pass)
VALUES ('$email', '$password')";