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 add a quantity property to your product and limit it to 2 and then enable the unique question option by going to Preferences and choosing which field do you want to setup as unique:
This way they only accept one submission with that value (it can be name, ID, ...)
You can try and clone this test form:
Please try to submit the same name 2 times.
Let us know if we can be of assistance.