How to add fields dynamically in custom form in Drupal 8 ?

Hello,

I have been trying to add couple of fields dynamically in a custom form in Drupal 8 but din't have luck till now. Could anyone please help me out !

The following is the ways I have tried with no luck

public function buildForm(array $form, FormStateInterface $form_state) {
    
	$form['#tree'] = TRUE;
	
	$form['names_fieldset'] = array(
    '#type' => 'fieldset',
    '#prefix' => '<div id="names-fieldset-wrapper">',
    '#suffix' => '</div>',
  );
	$num_names = $form_state->getValue('num_names');
	if (empty($num_names)) {
    $num_names = 1;
  }
	
	for ($i = 0; $i < $num_names; $i++) { 
	
	$form['names_fieldset'][$i] = array(
    '#prefix' => '<div class="two-col">',
    '#suffix' => '</div>'
    );
	
	$form['names_fieldset'][$i]['from'] = array(
      '#type' => 'textfield',
      '#title' => 'From',
      
      
    );
	
	$form['names_fieldset'][$i]['to'] = array(
      '#type' => 'textfield',
      '#title' => 'To',
      
    );
    	
	}
	
					
	$form['names_fieldset']['more_fields'] = array(
	    '#type' => 'submit',
	    '#value' => t('Add one'),
		'#submit' => array($this, 'modulename_add_more_add_one'),
	    '#ajax' => array(
			'callback' => array($this, 'modulename_add_more_callback'),
			'wrapper' => 'names-fieldset-wrapper',
		),
	);
	
	if ($num_names > 1) {
		
		$form['names_fieldset']['less_fields'] = array(
	    '#type' => 'submit',
	    '#value' => t('Remove one'),
		'#submit' => array($this, 'modulename_add_more_remove_one'),
	    '#ajax' => array(
			'callback' => array($this, 'modulename_add_more_callback'),
			'wrapper' => 'names-fieldset-wrapper',
		),
	);
		
	}
	
	$form['actions'] = array('#type' => 'actions'); 
		
	$form['actions']['submit'] = array( 
	'#type' => 'submit', 
	'#value' => t('Submit'),
	'#submit' => array($this, 'CustomSubmit'),	
	);
	
    return $form;
  }
  
  public function CustomSubmit(array &$form, FormStateInterface $form_state) {
	drupal_set_message("Custom Submit triggered");
	}
  
  public function modulename_add_more_callback(array &$form, FormStateInterface $form_state) {
		return $form['names_fieldset'];
	}
 
  public function modulename_add_more_add_one(array &$form, FormStateInterface $form_state) {
		$num_names++;
		$form_state['rebuild'] = TRUE;
	}
	
  public function modulename_add_more_remove_one(array &$form, FormStateInterface $form_state) {
		if ($num_names > 1) {
		$num_names--;
		}
		$form_state['rebuild'] = TRUE;
	}

Reference Used : Single field dynamically added in form in Drupal 8 (Provided by Drupal Contrib)
http://www.drupalcontrib.org/api/drupal/contributions%21examples%21form_example%21form_example_tutorial.inc/function/form_example_tutorial_9/8

Reference Used : Set of fields dynamically added in form in Drupal 7 (Provided by Drupal Contrib)
http://lovewithbug.com/technology/drupal/how-to-use-drupal-ajax-form-for-multiple-fields-with-add-more-concept/

Couple of the first issues using similar dynamic fields as mentioned in the article is using "$form_state['num_names']"

Error: Cannot use object of type Drupal\\Core\\Form\\FormState as array
&
PHP Fatal error:  Can't use method return value in write context