Warning: session_start(): Cannot start session when headers already sent in /var/www/html/libs/db.php on line 9

Fatal error: Uncaught Error: Call to undefined function mysqli_connect() in /var/www/html/libs/db.php:16 Stack trace: #0 /var/www/html/libs/db.php(28): DB->connect() #1 /var/www/html/libs/helper.php(7): DB->site('timezone') #2 /var/www/html/index.php(8): require_once('/var/www/html/l...') #3 {main} thrown in /var/www/html/libs/db.php on line 16