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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 have cloned and tested your form and I was able to reproduce error you are getting. After that I inspected your form and noticed that you have one additional Terms & Condition Widget inside of your form that is hidden and required. See screen shot below.
After removing it from mine cloned form I was able to submit the form. Try to do the same with your form.
Hope this will help. Let us know if you need further assistance.