I have issues with cookies in web-scraping - Flutter (Issues with cookies)

Question

GetAttendanceRequest() async {
  
var client = http.Client();
    
var posturl = Uri.parse('https://posturl');
var geturl = Uri.parse('https://geturl');
    
try {

// Getting the cookie 🍪

var postres = await client.post(posturl,body: {'password': 'pswd', 'userid': 'id'});
     

// saving the cookie in local variable

var RawCookiee = postres.headers.values.elementAt(2).toString().substring(0,42);
    

// Getting the attendance (web scraping my college website)

// the get request doesn't work it redirects me to the login page again (posturl)

var getres = await client.get(geturl, headers:{"Cookie": RawCookiee});
  dom.Document document = parser.parse(getres.body);
  final elements = document.getElementsByClassName("ibox");
  var Attendance = elements.map((element) => element.getElementsByTagName("h2")[0].innerHtml);

    var HoursCompleted = Attendance.toString().substring(9,11);
    var HoursAttended = Attendance.toString().substring(43,45);
    var Percentage = Attendance.toString().substring(47,52);
          
    
    } 
    finally {
      client.close();
    }
  }