src/Rules/AllowedFieldSets.php
protected function invalid(): Collection
    {
        if (!is_array($this->value)) {
            return collect();
        }

        return collect($this->value)->map(function ($value, $key) {
            return $this->notAllowed($key, $value);
        })->flatMap(function (Collection $fields, $type) {
            return $fields->map(function ($field) use ($type) {
                return "{$type}.{$field}";
            });
        });
    }
protected function invalid(): Collection
    {
        if (!is_array($this->value)) {
            return collect();
        }

        return collect($this->value)->map(function ($value, $key) {
            return $this->notAllowed($key, $value);
        })->flatMap(function (Collection $fields, $type) {
            return $fields->map(function ($field) use ($type) {
                return "{$type}.{$field}";
            });
        });
    }
Get the fields that are invalid.

@return Collection