Submit form to google sheet without reloading page and without jQuery using appscript doGet

I'm trying to submit data from html form to a google sheet, everything works correctly, but when I try to submit the form without reloading the page, the data is not displayed.I am trying to implement this in pure js without any libraries.

Apps Script code

var SHEET_KEY = '1IW8xdxivaSALFgUxGs9SIwAe07S6ZENEx-Ekr8l8aqU'
var SHEET_NAME = 'page1'
function doGet(e) {
  var lock = LockService.getPublicLock()
  try {
    var doc = SpreadsheetApp.openById(SHEET_KEY)
    var sheet = doc.getSheetByName(SHEET_NAME)
    var data = []
    data = [
      e.parameter['pr_name'],
      e.parameter['ing'],
      e.parameter['gramm'],
      e.parameter['class_p'],
    ]

    sheet.getRange(sheet.getLastRow() + 1, 1, 1, data.length).setValues([data])

    return ContentService.createTextOutput(
      JSON.stringify({ result: 'success' })
    ).setMimeType(ContentService.MimeType.JSON)
  } catch (e) {
    return ContentService.createTextOutput(
      JSON.stringify({ result: 'error', error: e })
    ).setMimeType(ContentService.MimeType.JSON)
  } finally {
    lock.releaseLock()
  }
}

html form

<form class="gform" method="GET" action="https://script.google.com/macros/s/AKfycbxoDeBDNJtnPkNxsMmWwIAT7ojRnxgzWBH-wHQnCmfWD6a-gsOdPrSopQ_fK3GJVtlw3w/exec" >
        <input type="text" name="pr_name" >
        <input type="text" name="ing">
        <input type="text" name="gramm">
        <input type="text" name="class_p">
        <input type="submit">
    </form>

js сode shows that everything works but data does not appear

let form = document.querySelector('form');

form.addEventListener('submit', function(evt) {
  evt.preventDefault();
  sendData();
});

 function sendData() {
    const XHR = new XMLHttpRequest();
    const FD = new FormData( form );

    XHR.addEventListener( "load", function(event) {
      alert( event.target.responseText );
    } );

    XHR.addEventListener( "error", function( event ) {
      alert( 'Oops! Something went wrong.' );
    } );

    XHR.open( "GET", "https://script.google.com/macros/s/AKfycbxoDeBDNJtnPkNxsMmWwIAT7ojRnxgzWBH-wHQnCmfWD6a-gsOdPrSopQ_fK3GJVtlw3w/exec" );

    XHR.send( FD );
  }

I get this response

{"result":"success","data":[null,null,null,null]}