Hi   I saw in the documentation that if we have multiple images file upload field the create post functionality may not work well with attaching an image to the featured image. Yes it doesn't work. So I tried adding this function in the functions.php file:  

function prefix_auto_featured_image() {
    global $post;
    if (!has_post_thumbnail($post->ID)) {
        $attached_image = get_children( "post_parent=$post->ID&post_type=attachment&post_mime_type=image&numberposts=1" );
         
      if ($attached_image) {
              foreach ($attached_image as $attachment_id => $attachment) {
                   set_post_thumbnail($post->ID, $attachment_id);
              }
         }
    }
}
add_action('the_post', 'prefix_auto_featured_image');
add_action('save_post', 'prefix_auto_featured_image');
add_action('draft_to_publish', 'prefix_auto_featured_image');
add_action('new_to_publish', 'prefix_auto_featured_image');
add_action('pending_to_publish', 'prefix_auto

}_featured_image');
add_action('future_to_publish', 'prefix_auto_featured_image');

  I am creating the posts in Draft mode so I can approve them. So when I receive the entry I make a post update and it should get the first image from the attachments as a featured. Yes, but it's not working unless I remove an invisible featured image that is attached by default and update the post. It's quite ok, but in the Formidable entries the image attachments are lost and they are visible only in the post.   Would be grateful for an advice how I can achieve a dynamic featured image from a multiple file upload field.   Thanks, Mariyan