Warning: Undefined variable $conn in /var/www/html/index.php on line 42

Fatal error: Uncaught TypeError: mysqli_close(): Argument #1 ($mysql) must be of type mysqli, null given in /var/www/html/index.php:42 Stack trace: #0 /var/www/html/index.php(42): mysqli_close(NULL) #1 {main} thrown in /var/www/html/index.php on line 42