Have you fixed the PayPal inventory control options problem?

It is not currently possible to limit the quantityof products that can be purchased, with payment tool wizard.

A workaround is to use one of our inventory widgets , Form calculation widget and donation option of payment field. You can perform calculation inside of your form and pass calculation to payment field.

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

https://www.jotform.com/help/301-How-to-Assign-Calculation-Value

Inside of this guide you can find out how to perform calculation in the form:

http://www.jotform.com/help/259-How-to-perform-calculation-in-the-form 

Here is a link to our inventory widgets:

http://widgets.jotform.com/widget/inventory 

http://widgets.jotform.com/widget/quantity_gift_registry 

http://widgets.jotform.com/widget/gift_registry