AJAX Requests and HubSpot Forms
So HubSpot don’t allow cross origin AJAX requests! This is only a problem because all of the tracking forms send to a generic forms.hubspot domain.
The way around this is to forward the request through a proxy or in other words just post the data to your own hosted script and literally forward it on to HubSpot’s original form action url.
Remember to add an SSL to the proxy endpoint if your HubSpot site is using https
For quick fixes like this we use Let’s Encrypt.