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.
Please check this user guide https://www.jotform.com/help/225-How-to-add-options-to-Payment-Forms
This is the part in the user guide that particularly described on how to
Check also the demo jotform included in the user guide http://www.jotformpro.com/form/30823446292959 . You can see the Quantity option
Hope this help. Inform us if you need assistance.