How can I insert data to the database?

I want to insert data from website but my website still can’t insert to database mysql. whats wrong with my php code?

this is the html file

<form class="sign-in-up-form" action="book.inc.php" method="POST">
                    <p class="section-title">Booking Form</p>
                    <input class="input-field" type="text" id="name" name="UserName" placeholder="Full name" required>
                    
                    <input class="input-field" type="tel" id="contact" name="UserContact" placeholder="Contact Number" required>
                    
                    <input class="input-field" type="email" id="email" name="UserEmail" placeholder="Email" required>
                    
                    <input id="datetime-book" class="input-field book-field" type="datetime-local" id="date" name="aptDateTime" required>
                    
                    <select class="input-field book-field" name="artistName" id="selArtist" required>
                        <option id="select-placeholder" value="">Please choose an artist</option>
                        <option value="Aurelius">Aurelius</option>
                        <option value="Crocks">Crocks</option>
                    </select>

                    <textarea id="textarea-tattoo-idea" name="aptComment" class="input-field" placeholder="Describe your tattoo idea here..."></textarea>

                    <input class="submit-btn" type="submit" name="submit" value="book">
                </form>

this is the php file

<?php
session_start();
// connect to database

$con = mysqli_connect("localhost","root","","yellowstudios");

if (empty($_POST["UserName"])) {
    die("Name is required");
}

if (!filter_var($_POST["UserEmail"], FILTER_VALIDATE_EMAIL)) {
    die("Valid email is required");
}

// to collect data
if(isset($_POST['submit'])) {

    $UserName = $_POST['UserName'];
    $UserContact = $_POST['UserContact'];
    $UserEmail = $_POST['UserEmail'];
    $aptDateTime = $_POST['aptDateTime'];
    $artistName = $_POST['artistName'];
    $aptComment = $_POST['aptComment'];

    // will insert to DB
    $query = "INSERT INTO bookDB (UserName, UserContact, UserEmail, aptDateTime, artistName, aptComment, aptStat) VALUES ('$UserName', '$UserContact', '$UserEmail', $aptDateTime','$artistName', '$aptComment', ?)";
    $query_run = mysqli_query($con, $query);

    if($query_run)
    {
        // will execute if booking is successful, and will go to next page
        $_SESSION['status'] = "Appointment inserted successfully!";
        header("Location: book.output.php");
    }
    else
    {
        // will execute if booking is not successful, and will go to next page
        $_SESSION['status'] = "Appointment not inserted!";
        header("Location: book.output.php");
    }
}

I looked for typos and everything, but it won’t insert data to database. I also double checked everything.