Hubspot embbed script : Uncaught TypeError: Cannot read properties of undefined (reading 'value')

Question

We have this custom script for our hubspot contact form that basically redirects the contact to an other page and saving the filled contact informations as a query string in the url.

The script was working fine until today but it seems to not work anymore...

Here is the script :

<!-- this is the standard form embed code --> 
<!--[if lte IE 8]>
<script charset="utf-8" type="text/javascript" src="//js.hsforms.net/forms/v2-legacy.js"></script>
<![endif]-->
<script charset="utf-8" type="text/javascript" src="//js.hsforms.net/forms/v2.js"></script>
<script>
  hbspt.forms.create({
    region: "na1",
    portalId: "6914456",
    formId: "a29bb11e-d9d1-4ffd-a8f7-9e8038cad4c9"
  });
  // add custom script after it
  var array = [];
  window.addEventListener('message', event => {
    // in the onFormSubmit global form event, grab the data and push it to the above array
    if(event.data.type === 'hsFormCallback' && event.data.eventName === 'onFormSubmit') {
      let vars = ['irstname', 'lastname', 'email'];
      let len = vars.length;
      for (i = 0; i < len; i++) {
        for (j in event.data.data) {
          if (event.data.data[j]["name"] == vars[i]) {
            let object = {
              name: '',
              value: ''
            };
            object.name = vars[i];
            object.value = event.data.data[j]["value"];
            array.push(object);
          }
        }
      }
    }
    // after the form has submitted and data sent to Hubspot, get the data from the array and then redirect the page, adding the data to the URL
    if(event.data.type === 'hsFormCallback' && event.data.eventName === 'onFormSubmitted') {
      var firstname = array[0].value
      var lastname = array[1].value
      var email = array[2].value
      window.location = "https://cleverconnect.com?firstName=" + encodeURIComponent( firstname ) +"&lastName=" + encodeURIComponent( lastname ) +"&email=" + encodeURIComponent( email );
    }
  });
</script>

And we get this error in the console

(index):278 Uncaught TypeError: Cannot read properties of undefined (reading 'value')
    at (index):278:32

Does someone know why it doesn't work, although we didn't change anything.

Thanks a lot !