how to debug?

debbug

function debug_this($args) {
   print_r($args);
}

add_filter( 'attachment_fields_to_save', 'RE_attachment_field_version_save', 10, 2 );
function RE_attachment_field_version_save( $post, $attachment ) { 

   debug_this(get_post_ancestors($post['ID']));
   
   if( isset( $attachment['re-current-version'] ) ) { 
      //let's remove the current version setting in the db for this attachment type
      //update_post_meta( get_post_ancestors($post['ID'])[0]), 're-current-version', $attachment['re-current-version'] );
      //update_post_meta( $post['ID'], 're-currnt-version', 0 );
      update_post_meta( $post['ID'], 're-current-version', $attachment['re-current-version'] );
   }   

   return $post;
}