public function buildFormDataString($options)
    {
        $options = $this->resolve($options);
        $formOptions = [];

        foreach ($this->formParameters as $key => $isFormParameter) {
            if ($isFormParameter && isset($options[$key])) {
                $formOptions[$key] = $options[$key];
            }
        }

        return http_build_query($formOptions);
    }