Warning: Undefined variable $mysqli in /opt/revival/profile.php on line 15

Fatal error: Uncaught TypeError: mysqli_query(): Argument #1 ($mysql) must be of type mysqli, null given in /opt/revival/profile.php:15 Stack trace: #0 /opt/revival/profile.php(15): mysqli_query() #1 {main} thrown in /opt/revival/profile.php on line 15