Populate Product quantity from field on jotform

Unfortunately, it is not possible to populate product quantity of payment field. If you need to calculate quantity based on users answers, I would suggest to re-create products with standard form elements and set up calculations on the form. The total can be then passed to payment field: How-to-Pass-a-Calculation-to-a-Payment-Field

Hope this helps! But, please get back to us if you need further assistance.