I want to store data in a variable in echo

I`m just sharing my code below

    echo "
                
            <div class='student-input'>
                <input type='text' id='fee' class='form-control' name='fee' value='$fee'>
            </div>
            
";

Here I want to fetch the input data but as it is in echo, php can`t read my $fee=$_post method, how could I store the input data into a variable? so that I could pass the value to another file

   <h2>Student Approval</h2>
    <form method='post'>
            <?php $servername="localhost";
        $username="root";
        $password="";
        $database="itswebycom_Registration";
        
        //create connection
        $conn = new mysqli($servername,$username,$password,$database);
    $successMessage="";
     $name= $_SESSION ['auth_user']['name'];
      $id= $_SESSION ['auth_user']['id'];
        
         if ($_SERVER['REQUEST_METHOD']=='GET'|| $_SERVER['REQUEST_METHOD']=='POST' ){
        
         $sql1="SELECT * FROM student_reg_pending WHERE ins_name='$name' and ins_id='$id' ";
            $result1= $conn->query($sql1);
            
            if(!$result1){
            
            die("Invalid query: ".$connection->error);
            
        }
        
            while($row=$result1->fetch_assoc()){
     $fee="";
        
        
        
        echo "
        
    
    
                <div class='student-row'>
            <div class='student-name'>$row[name]</div>
            
            
            <div class='student-input'>
                <input type='text' id='fee' class='form-control' name='fee' value='$fee'>
            </div>
            
          

            <div class='student-buttons'>
                <button class='approve-btn' type='submit' name='approve' id='approve'><a href='stu-reg.php?fee=$f & name=$row[name] & pending=approve & ins_name=$row[ins_name] & ins_id=$row[ins_id]'>Approve</a></button>
                <button class='decline-btn' name='decline' type='submit' id='decline'><a href='stu-reg.php?name=$row[name] & pending=decline & ins_name=$row[ins_name] & ins_id=$row[ins_id]'>Decline</a></button>
            </div>
        
        </div>
        
        
            ";
            } } ?></form></div>

echo "
    


            <div class='student-row'>
        <div class='student-name'>$row[name]</div>
        
        
        <div class='student-input'>
            <input type='text' id='fee' class='form-control' name='fee' value='$fee'>
        </div>
        ";

i have tried $fee=$_POST[‘fee’]; but the didn`t get stored and shows undefined variable fee