What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
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I did test your form which is embedded in your webpage and thank you page is being displayed but you need to scroll to view the thank you message. Please check the screenshot below:
I would suggest you to please embed your form using its iFrame embed code and see if that solves your problem. The following guide should help you how to grab your form's iFrame embed code: http://www.jotform.com/help/148-Getting-the-Form-iFrame-Code
Hope this helps.
Do get back to us if the issue persists.