How to send amp-state when submitting the form from amp email?

Question

<form method="post" action-xhr="url_goes_here">
        <input hidden name="foo" value="bar" [value]="details">
</form>

I want to send states in amp-email form, I have a hidden input  This details is a dict with all the data stored in the states that I want.

This is what I get on the backend from the request

ImmutableMultiDict([('foo', 'bar')])