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.
Unfortunately, you cannot pass a custom calculation to the payment wizard that has products setup on it.
If you want to pass a calculation value to the payment wizard, you need to change the "Payment Type" from "Sell Products" to "User Defined Amount". You can learn more about this on this guide: https://www.jotform.com/help/275-How-to-Pass-a-Calculation-to-a-Payment-Field
With that, you'll need to recreate the existing products on your payment wizard to the default form fields in the form.
I hope that helps.