RESTful Web Services : How to simply post a paragraph entity
Finally, seems it comes from Paragraph module, file ParagraphAccessControlHandler.php function checkCreateAccess :

  protected function checkCreateAccess(AccountInterface $account, array $context, $entity_bundle = NULL) {
// Allow paragraph entities to be created in the context of entity forms.
if (\Drupal::requestStack()-&gt;getCurrentRequest()-&gt;getRequestFormat() === 'html') {
  return AccessResult::allowed()-&gt;addCacheContexts(['request_format']);
}
return AccessResult::neutral()-&gt;addCacheContexts(['request_format']);


}

Code goes in the second return as request format is not html but json. If I force the return to be AccessResult::allowed(), the paragraph is created. Why this restriction to forms ? How to overwrite this without patching ?