I'm trying to build a custom form and submission post for Hubspot.

I have the following code

HTML

  

    

      
    
    Sign up
  

  
  

    
    

    
    
  

JS (prezzi-form-submit.js)

// // Send form data to HubSpot from the client.
function submitToHubSpot(data) {
  var $form = $('#hubspot-form form'),
      k;

  // Loop through each value and find a matching input.
  // NOTE: Doesn't support checkbox/radio.
  for (k in data) {
    $form.find("input[name='" + k + "']").val(data[k]);
  }

  $("form input:submit").trigger("click");
}

// Here's how you'd use this.
$('#my-custom-form').on('submit', function() {
  var formData = {};
  $(this).serializeArray().forEach(function(data) {
    formData[data.name] = data.value;
  });

  submitToHubSpot(formData);

  // We sent the data. Now do whatever else you want.
  alert('Gee, thanks Jonathan! Now I can focus on onboarding my customers with Appcues!');
  window.location.href = 'http://appcues.com';
})

When I press the submit button, I get the following error in the console

Blocked form submission to " " because the form's frame is sandboxed and the 'allow-forms' permission is not set.

As you can see I have the

sandbox="allow-forms"

set in the I frame but it isn't working. How can I fix this error?