Marketo's Native Known Visitor Custom HTML is not submiting.
I have the following page with a form that has the Known Visitor Custom HTML enabled.
https://go.forsta.com/KV-HTML-Test.html
I haven't added anything extra other than the standard four tokens it suggests.
The form loads as expected for known visitors.
However it doesn't allow me to submit.
When trying to submit the button stays as it is. When attempting to submit I get the following error.

Any idea why? These KV HTMLs used to work well a while ago. Haven't tested it recently so I'm not sure when it became non-responsive.