HTTP Request from Logic not being made

Hi there.
Link to read only site here

I have a test-site with a form that accepts a code. I am running an n8n based test-API that returns 200 if the code is “1234” and 404 for any other value. Both responses also return a message body (simple JSON).

If I integrate with this API using a form that has direct access to the API, it works as expected. Entering 1234 results in a Success message being presented on the test-site. Any other value presents a failure message.

My current attempt at an integration via Logic appears to work when I select Test Flow in that it makes the HTTP request on the n8n end-point. However when using this logic-form from published test-site, it returns immediately with a success 200. It does not even attempt to use the API.

I must be missing something obvious here. Any help would be welcomed.