wp_insert_post not working

I guess the reason is you have not added post title and added post id

$my_post = array(
                'post_id' => 1,
                'post_status' => 'pending',
                'post_type' => 'post'
            );

Ideally if should be

$my_post = array(
  'post_title'    => wp_strip_all_tags( $_POST['post_title'] ),
  'post_content'  => $_POST['post_content'],
  'post_status'   => 'publish',
  'post_author'   => 1,
  'post_category' => array( 8,39 ),
'post_type' => 'post'
);