How to I create an item with limited stock?

I run classes and can only enroll 12 students. Can't go over. How can I limit the amount sold?

Unfortunately, we don't have any built-in solution for this one in our payment tools; but you can achieve this scenario by using the combination "Inventory" widget, "Form Calculation" widget and one of the payment tools. Below, you will find a guide about how to do that:

http://www.jotform.com/help/275-How-to-pass-a-calculation-to-a-payment-field

If you stuck or need extra information, please let us know.