public function getErrorMessage()
    {
        if (array_key_exists('error', $this->responseData?: [])) {
            if (is_string($this->responseData['error'])) {
                return json_encode($this->responseData['error']);
            } elseif(array_key_exists('error', $this->responseData['error'])) {
                return json_encode($this->responseData['error']['error']);
            } else {
                return json_encode($this->responseData['error']);
            }
        } else {
            return null;
        }
    }