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 do that with any of our payment tools, including a Purchase Order integration, then you can add the product and add a Quantity Property and mark the Custom Quantity (Text Box)
Please check this guide for further details, and let us know if you have doubts so we can gladly assist you
Though there is already a demo in that guide, I made another demo form for you to see how it would look like