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 a test submission on your direct form and I didn't encounter any issues with it. After hitting the submit button, it redirected me to the Thank You page.
If this form is embedded on a webpage, please try re-embedding the it using the Iframe method. Here's a guide: https://www.jotform.com/help/148-Getting-the-form-iFrame-code
If the issue is still the same, let us know. Please provide that webpage URL where the form is embedded. Thank you.