Hey there,
Apologies for the long delay in responding here. Are you still running into this? If so, it would be great to see an x-nf-request-id for the POST request that the browser makes when you submit to your form. If you have any questions about how to get that, please let us know!
Also wanted to share a bit about how our form action works: our form parser looks for the elements of your form when we build your site. Then, our forms accept data in the shape of the form that we set up for you during your build. For the action in particular, our form parser takes whatever path you put there and, on submission, serves the page located at that path.
I’ve seen other people have issues with a dynamic action element, so I’m not sure it’s actually possible to use it that way. A workaround would be to use Gatsby’s navigate utility to do a client-side route to the correct path. Here’s an example:
// On success, redirect to the custom success page using Gatsby's `navigate` helper function
.then(() => navigate("/thank-you/"))
// On error, show the error in an alert
.catch(error => alert(error));
};