am getting CORS error while posting data from front end

Question

i am getting "Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://"myurl". (Reason: CORS header ‘Access-Control-Allow-Origin’ missing). Status code: 504" here is my API

createGroup(language, req, callback) {
let data = req.body;

if(req.file){

  const csvFilePath = req.file.path;
 
  var username=
  csv()
    .fromFile(csvFilePath)
    .then((jsonObj) => {
      
      var array1 = [];
      for (let i = 0; i < jsonObj.length; i++) {

        array1.push(jsonObj[i].phoneNumber);
      }
      UserCollection.find({ mobile: { $in: array1 } }, function (err, docs) {
        if (err) {
          console.log(err)
        }
        else {
          // console.log(docs[0]._id);
          var array2 = [];
          for (let i = 0; i < docs.length; i++) {
            array2.push(docs[i]._id.toString());
          }
          

          let groupObj = new Group({
            groupName: data.groupName,
            users: array2,
            courses: [],
            effectiveDate: data.effectiveDate,
            effectiveStatus: data.effectiveStatus,
            createdBy:ObjectId(req.id)
          });
         
          groupObj.save((error, result) => {
            if (error) {
              return callback(false, common.errorMsg("Went wrong"));
            }
            return callback(false, common.successMsg("GROUP CREATED", {}));
          });
        }
      });

    }
    )
}else{
  let groupObj = new Group({
    groupName: data.groupName,
    users: data.users,  //.split(","),
    courses: [],
    effectiveDate: data.effectiveDate,
    effectiveStatus: data.effectiveStatus,
    createdBy:ObjectId(req.id)
  });
  
  groupObj.save((error, result) => {
    if (error) {
      console.log(error)
      return callback(false, common.errorMsg("Went wrong"));
    }
    return callback(false, common.successMsg("GROUP CREATED", {}));
  });
}
  

};

here is the post request i am sending from front end

groupName: testing users: 61937f894f95f04da73cc586 effectiveStatus: 1 effectiveDate: Fri Aug 19 2022 files: