Passing value from a view to a controller using codeigniter 4 not working

Using codeigniter 4 (PHP) and javascript for the modal. I am trying to pass the value of "rjuid" (html input type hidden) to the controller variable $uid, but I always get NULL value for $uid.

This is my code in view under a modal.

<div class="modal fade" id="RejoinModal" tabindex="-1" role="dialog" aria-labelledby="reJoinModalLabel" aria-hidden="true">
      <div class="modal-dialog">
        <div class="modal-content">
          <?php
          $attributes = ['class' => 'frmReJoinUser', 'id' => 'frmRJTUid'];
          echo form_open('rejoin_term_user', $attributes); 
          ?>        
        <div class="modal-header">
            <button type="button" class="close" data-dismiss="modal" aria-label="Close"><span aria-hidden="true">&times;</span></button>
            <h4 class="modal-title" id="reJoinModalLabel">Rejoin User</h4>
        </div>  
        
        <div class="modal-body">
              <?php
              $data = [
                 'type'  => 'hidden',
                 'name'  => 'rjuid',
                 'id'    => 'rjuid',
                 'value' => '',
                 'class' => 'form-control',
              ]; 
              echo form_input($data); 
              ?>                
        
            <div class="form-group">
                <label for="rejoin_date">Rejoin Date:</label>
                <input type="date" class="form-control" id="rejoin_date" placeholder="Enter Rejoin Date" name="rejoin_date" required>
            </div>
        
            <div class="form-group">
                <label for="name">Remarks (if any):</label>
                <textarea rows="2" cols="50" class="form-control" id="remarks" placeholder="Enter Remarks" name="remarks"></textarea>
            </div>
        </div>         
          
        <div class="modal-footer">
            <button type="button" class="btn btn-default" data-bs-dismiss="modal">Close</button>
            <button type="submit" id='btnReJoinTermUser' class="btn btn-primary">Rejoin user</button>
          </div>
          
        <?php echo form_close(); ?>
        
        </div>
       </div>
    </div>

This is my controller (rejoin_term_user.php)

public function rejoin_term_user(){ 
$request = \Config\Services::request();
echo "<h1> Rejoin Term </h1>";
    
$uid = $request->getPost('rjuid');
// $uid = $this->request->getPost('rjuid');
// $uid = $this->request->getVar('rjuid');
// $uid = $this->request->getPostGet('rjuid');
dd($uid);

}

Note: I already tried those codes that are commented in the controller, but still I get Null value for $uid.