// Validate credentials
        if ($unique_code_err == "") {
            // Prepare a select statement
            $sql = "SELECT id, unique_code FROM users WHERE unique_code = :unique_code";

            if ($stmt = $pdo->prepare($sql)) {
                // Bind variables to the prepared statement as parameters
                $stmt->bindParam(":unique_code", $param_unique_code, PDO::PARAM_INT);

                // Set parameters
                $param_unique_code = trim($_POST["unique_code"]);

                // Attempt to execute the prepared statement
                if ($stmt->execute()) {
                    // Check if username exists, if yes then verify password
                    if ($stmt->rowCount() == 1) {
                        if ($row = $stmt->fetch()) {
                            $id = $row["id"];
                            $unique_code = $row["unique_code"];
                                // Password is correct, so start a new session
                                session_start();

                                // Store data in session variables
                                $_SESSION["loggedin"] = true;
                                $_SESSION["guestloggedin"] = true;
                                $_SESSION["idguest"] = $id;
                                $_SESSION["unique_code"] = $unique_code;

                                // Redirect user to welcome page
                                header("location: wishlist.php");
                        }
                    } else {
                        // Display an error message if username doesn't exist
                        $unique_code_err = "This unique code does not exist.";
                    }
                } else {
                    echo "Oops! Something went wrong. Please try again later.";
                }

                // Close statement
                unset($stmt);
            }
        }

        // Close connection
        unset($pdo);
    }
}
?>