JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
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.
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:
If you stuck or need extra information, please let us know.