I was just about to merge your code with this account, but I'm glad you worked it out. I have no Idea why it didn't work there, it's essentially the same form.
This sound like that the ajax request is halted somewhere or denied completely. Do you have any kind of .htaccess login or similar authentication activated? It can block the ajax request as it cannot authenticate itself on server level.
Do you have an url where I can see this in action?Best,
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