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Upon checking your web page, I was able to replicate the problem you are having but when I tested your form with its direct URL, I was not able to replicate the issue you are having with your embedded form. The next button and validation works just fine. Please check the screenshot below:
There seems to be some conflict between form scripts and other scripts of your web page. I would suggest you to please embed your form using your form's iFrame embed code. The following guide should help you grab iFrame code of your form: https://www.jotform.com/help/148-Getting-the-Form-iFrame-Code
Hope this helps.
Do get back to us if the issue persists.