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.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
You can set a Unique Submission in your form. This will prevent multiple submissions from the same IP or same browser. Here's a guide: How-to-Set-Unique-Submissions-on-a-Form
You may also set a Unique Question so that the same value entered in the field will not be allowed to submit anymore. Here's a guide: How-to-set-Form-Limits-Based-on-a-Unique-Question
Hope this helps. If you have any questions, let us know. Thank you.