Issue creating database for a HTML Form using PHP [duplicate]

I am creating my CV website and am creating a contact me form at the bottom of my website. So I am using HTML, CSS, PHP and Java to help me with this. Basically, I want to create a database in myPHP within Hostinger as my server to view and download people’s entries. I am having trouble getting the HTML to communicate with PHP to make it work properly.

I’ve tried using formsubmit but it times out so frequently so I am opting to learn PHP and use this as a learning tool. My issue is I get a HTTP 405 or 500 error after I hit the submit button. Can someone help me with my PHP code please? I will post both HTML and PHP. The HTML code is in a file called form.html and the PHP code is inside the file dbnew.php. Thanks in advance

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <form action="dbnew.php" method="POST">
        <div class="input-box">
            <div class="input-field">
                <label for="fullName">
                <input type="text" name="fullName" placeholder="Full Name" required>
                <span class="focus"></span>
                </label>
            </div>
            <div class="input-field">
                <label for="email">
                <input name="email" type="email" id="email" pattern="/^[a-zA-Z0-9.!#$%&*+/=?^_`{|}~-]+@[a-zA-Z0-9-]+(?:.[a-zA-Z0-9-]+)*$/" placeholder="Email Address" required>
                <span class="focus"></span>
                </label>
            </div>
        </div>
            <div class="input-box">
                <div class="input-field">
                    <label for="phone">
                    <input type="tel" id="phone" name="phone" placeholder="Phone Number" required>
                    <span class="focus"></span>
                    </label>
                </div>
            
                <div class="input-field">
                <label for="emailSubject">
                <input type="text" name="emailSubject" placeholder="Email Subject" required>
                <span class="focus"></span>
                </label>
                </div>
            </div>
            <div class="textarea-field">
                <textarea name="emailMessage" id="" cols="30" rows="10" name="message" placeholder="Your Message" required></textarea>
                <span class="focus"></span>
                
            </div>

            <div class="btn-box btns">
                <button type="submit" class="btn">Submit</button>
            </div>
            
    </form>
</body>
</html>
<?php
 $fullName = $_POST['fullName'];
 $email = $_POST['email'];
 $phone = $_POST['phone'];
 $emailSubject = $_POST['emailSubject'];
 $emailMessage = $_POST['emailMessage'];

 if (!empty($fullName) || !empty($email) || !empty($phone) || !empty($emailSubject) || !empty($emailMessage)){
    $servername = "https://mywebsite.com";
    $database = "u292472425_mywebsite";
    $username = "u42424823_username";
    $password = "MyPassword#1234";


 
    // Create connection
$conn = new mysqli($servername, $username, $password, $database);
if (mysqli_connect_error()) {
        
            die('Connection error('. mysqli_connect_errno().')'. mysqli_connect_error());
        
        }else{
            $SELECT = "SELECT email From register Where email = ? Limit = 1";
            $INSERT = "INSERT Into register (fullName, email, phone, emailSubject, emailMessage) values(?, ?, ?, ?, ?)";
    
        $stmt = $conn->prepare($SELECT);
        $stmt->bind_param("s", $email);
        $stmt->execute();
        $stmt->bind_result($email);
        $stmt->store_result();
        $rnum = $stmt->num_rows;

        if ($rnum==0) {
            $stmt->close();

            $stmt = $conn->prepare($INSERT);
            $stmt->bind_param("ssiss", $fullName, $email, $phone, $emailSubject, $emailMessage);
            $stmt->execute();
            echo "New record inserted successfully";
        } else {
            echo "Someone already registered using this email";
        }
        $stmt->close();
        $conn->close();

        }
    } else{
        echo "All fields are required";
        die();
    }
?>