capture $_POST on specific page w/ Elementor widget of matching ID

functions.php

if ( ! function_exists('write_log')) {
   function write_log ( $log )  {
      if ( is_array( $log ) || is_object( $log ) ) {
         error_log( print_r( $log, true ) );
      } else {
         error_log( $log );
      }
   }
}

add_action( 'elementor/frontend/section/before_render', function ( \Elementor\Element_Base $element ) {
    if ( is_page('my-special-page') && $element->get_settings('_element_id') === 'unique-id' ) {
    write_log('start');
    write_log($_POST['fields']['field_id']['value']);
    write_log('end');
  }
});