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The Payment Tools do not have their own inventory managment module. So it will be difficult to have this feature using only the Form Builder.
However, you may want to use the Inventory Widget instead and combine it with the Payment Tool to have inventory functionality and payment/order function as well.
Here is the demo Inventory Form you can test http://form.jotformpro.com/form/51413853223953?
If you submit the form, you will see the invenroty available balance get updated.