html - how to redirect a page using php

    define('DB_PASS' ,'');
    define('DB_NAME', 'codexworld');
    $con = mysqli_connect(DB_SERVER,DB_USER,DB_PASS,DB_NAME);
    if(isset($_POST['submit'])){

    $username=$_POST['username'];
    $email=$_POST['email'];
    $subject=$_POST['subject'];
    $message=$_POST['message'];
    $q=mysqli_query($con,"insert into demo (username,email,subject,message)values('$username','$email','$subject','$message')");
    if ($q){
    echo 'Not Inserted';
    } else {
    echo 'Inserted Successfully';
    header('Location: ib.php');

    }
    }
    ?>
    
    
       
          
          
          
       

       
          

             

                

                   
Contact Us
                   

                      Name
                      
                   
                   


                      Email address
                      
                   
                   

                      Subject
                      
                   
                   
                   
                

             
          
       
    

the above code connects to database and saves form data in database and it is supposed to redirect
the form data gets stored in data base but it doesn't redirect.
How can i solve this?Save the form data and redirect