my code was running well before i host my web now i see this kind of error after web being hosted. please help me [closed]

Warning: mysqli_query() expects parameter 1 to be mysqli, null given in /category.php on line 14

Fatal error: Uncaught Error: Call to a member function error() on null in category/category.php:20 Stack trace: #0 {main} thrown in category/category.php on line 20

<?php
session_start();
mysqli_report(E_ALL);
if(!isset($_SESSION['loggedin'])){
    header('location : ../../connection/session.php');
    exit();
}
 if(isset($_POST["submit"])){
   if(empty($_POST['name'])){
      echo "some fields are empty";
   }else{
        $names = $_POST['name'];

      $result= mysqli_query($link,"insert into category(name) values('$name')");
        
      if($result){
          echo "added successfully";
      header('location:create.php');
   }else{
       echo "error".$link->error();
   }
   }
   }