Components filled with Tampermonkey script are not recognized as filled

I filled out the registration form on the site https://register.gotowebinar.com/register/2965111702634965004 automatically with a script.

// ==UserScript==
// @name         Duolos autofill registration form
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  try to take over the world!
// @author       blaz
// @match        https://register.gotowebinar.com/register/*
// @icon         https://www.google.com/s2/favicons?sz=64&domain=gotowebinar.com
// @grant        none
// @run-at       document-end
// ==/UserScript==

setTimeout(function(){
console.log("10s later...");

var formFirstName = document.getElementById('registrant.firstName')
var formEmail = document.getElementById('registrant.email')

formFirstName.value = 'My_first_name'
formEmail.value = '[email protected]'

}, 10000);

However, when I want to confirm the form with the button on the page, I get a message that the fields filled in by the script have no content and I have to fill them in to go further. Is there any way around it?

required fields