Problem connecting to DB via Ionos hosting service

I’m trying to set up a subscriber emailing list on my website. The php code appears to work on my localhost but not on the live server.

Nothing is appearing in the DB????

Here’s my code:

<?php
if (isset($_POST['Subscribe'])) { 
    // Assuming the submit button/hidden field name is "Subscribe"
    $userEmail = $_POST['email'];

    // Validate email address (optional but recommended)
    if (filter_var($userEmail, FILTER_VALIDATE_EMAIL)) {
        // Database configuration (replace sensitive details with environment variables)
        $servername = "db5016690051.hosting-data.io";
        $username = "dbu2398034";
        $password = "xxxxxxxxxxx";
        $dbname = "dbs13515622";

        // Create connection
        $conn = new mysqli($servername, $username, $password, $dbname);

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

        // Prepare and execute an SQL statement to insert the email into the database
        $sql = "INSERT INTO `subscriber` (email) VALUES (?)";
        $stmt = $conn->prepare($sql);

        if ($stmt) {
            $stmt->bind_param("s", $userEmail);

            try {
                $stmt->execute();
                echo '<p>Email address successfully added to the list.</p>';
            } catch (Exception $e) {
                echo '<p>Error adding email address: ' . htmlspecialchars($e->getMessage()) . '</p>';
            }

            $stmt->close();
        } else {
            echo '<p>Failed to prepare the SQL statement.</p>';
        }

        // Close the connection
        $conn->close();
    } else {
        echo '<p>Invalid email address. Please try again.</p>';
    }
}
?>

I have tried different codes, Ionos help line and nothing is working!