getting XMLHttpRequest error when running http request in flutter web

Question

I am trying to add data to google sheets but when I run an HTTP request it says

in console(chrome): No 'Access-Control-Allow-Origin' header is present on the requested resource.
in terminal: XMLHttpRequest error.

plzz let me know the appropriate code change.

App script for google sheet.

function doGet(request) {
  var sheet=SpreadsheetApp.openById("1t_QhI26mDTn1dGSA0CwZG0SiCuWvascascascsac");
  var result={"status":"success"};

              try{

             var LrNo=request.parameter.lrNo;
             var PhoneNo=request.parameter.phoneNo;

              var rowData=sheet.appendRow([LrNo,PhoneNo]);
             }catch(exc){
              result={"status":"Failed","mesage":exc};
             }

return ContentService
.createTextOutput(JSON.stringify(result))
.setMimeType(ContentService.MimeType.JSON);


}

Code to fetch data.

class FormService {
  static const String firstLink =
      "https://script.google.com/macros/s/AKfycbzUobmwvXUsBlh-uZtBJ4Uw76tL5nhuKZfiH4_Wg/exec";

  String getLink() {
    return "?LrNo=${TextFieldData.lrNO}&PhoneNo=${TextFieldData.phoneNo}";
  }

  Future<void> submitForm() async {
    try {
      await http.get(firstLink + getLink()).then((response) {
        print(response.statusCode);
      });
      //print(kk.statusCode);
    } catch (e) {
      print(e);
    }
  }
}