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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.