Removed Duplicate HTML Tags: Eliminated the extra and tags to ensure valid HTML structure. Removed Duplicate JavaScript: Consolidated the JavaScript code, removing the redundant copy at the end of the file. Fixed SQL Query: Removed lastname from the SQL INSERT query since the form does not collect this field, preventing potential database errors. Improved Validation: Consolidated validation logic using array_filter to collect errors, making the code more concise and maintainable. Removed Commented-Out Code: Eliminated incomplete validation fragments (e.g., elseif (!filter_var($email, FILTER_VALIDATE_EMAIL))) to avoid confusion and ensure reliance on the validateEmail function. Escaped Output: Added htmlspecialchars to the page title to prevent potential XSS attacks. Security Note: While not implemented here, consider adding CSRF protection (e.g., a CSRF token) to the form for enhanced security. This would require additional changes to the form and validation logic.