code: protected function notAllowed(string $resourceType, string $fields): Collection
      {
          $fields = collect(explode(',', $fields));
  
          if (!$this->allowed->has($resourceType)) {
              return $fields;
          }
  
          $allowed = $this->allowed->get($resourceType);
  
          if (is_null($allowed)) {
              return collect();
          }
  
          $allowed = collect((array) $allowed);
  
          return $fields->reject(function ($value) use ($allowed) {
              return $allowed->contains($value);
          });
      }
docs: Get the invalid fields for the resource type.
  
  @param string $resourceType
  @param string $fields
  @return Collection