bs_flutter_selectbox save multiple values

Question

final BsSelectBoxController _stID = BsSelectBoxController(multiple: true);

  Future<BsSelectBoxResponse> selectApi(Map<String, dynamic> params) async {
    final response =
        await http.get(Uri.parse('https://fasl.chabafarm.com/api/sss'));

    if (response.statusCode == 200) {
      List json = convert.jsonDecode(response.body);
      return BsSelectBoxResponse.createFromJson(json,
          value: (data) => data['id'],
          renderText: (data) => Text(data['title']));
    }

    return BsSelectBoxResponse(options: []);
  }

enter image description here I want to know how to send multiple values How to declare variables?