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.
In your current configuration, it's not possible. You will have to go for a workaround such as using the inventory widget to configure the product items.
This means that you will have to add the items one after another. You have sub-product items, this also means that you have to add them individually.
You can clone the demo form for you to see how the inventory widgets are totaled.
Demo form: https://form.jotform.com/61471146729964.
Let us know if you have questions about the setup.