Inline Entity Form - Simple not available for storage entities referenced via storage entities

The simple widget plugin's implementation has an Drupal\inline_entity_form\Plugin\Field\FieldWidget\InlineEntityFormSimple::isApplicable method implemented as follows:

/**
   * {@inheritdoc}
   */
  public static function isApplicable(FieldDefinitionInterface $field_definition) {
    $handler_settings = $field_definition->getSettings()['handler_settings'];
    $target_entity_type_id = $field_definition->getFieldStorageDefinition()->getSetting('target_type');
    $target_entity_type = \Drupal::entityTypeManager()->getDefinition($target_entity_type_id);
    // The target entity type doesn't use bundles, no need to validate them.
    if (!$target_entity_type->getKey('bundle')) {
      return TRUE;
    }

    if (empty($handler_settings['target_bundles'])) {
      return FALSE;
    }

    if (count($handler_settings['target_bundles']) != 1) {
      return FALSE;
    }

    return TRUE;
  }

So maybe you are either referencing to no Storage type at all or are allowing more than one type? Nevertheless, this is most probably a problem of Inline Entity Form module and not Storage Entities. Closing as duplicate in favor of 🐛 Storage Entities - Simple not available for storage entities referenced via storage entities Active . If for some reason this is actually a problem originated by Storage Entities, feel free to re-open.

Ah that's it, I'm referencing more than one type, maybe I'll update the readme on inline entity to clarify that simple won't work for more than one entity type reference