Not clear how additional Shipping items and marginal costs for adding these items in shopping cart work

I have 7-8 Products... shipping cist for 1st item is $25.00 then adding additional items should increase shipping costs, per order, by $10.00...this  does not seem to work as the order total is not adjusted properly.

 

See think ink https://screencast.com/t/9Xg3hECsFlK

I've reviewed your form and I can see what you're referring to, basically the "Additional Item Cost" only works when your product has a quantity field in it, the "First item cost" will be always applied since even if you do not have a quantity field in your product the purchased quantity will be always 1. 

This can bee seen if you add the quantity option to your form, example: 

The shipping cost will be increase if you add an additional item: 

You will see how it works on this cloned form of yours: https://www.jotformpro.com/form/71016854101950 

You could also refer to the following guide in order to get more info about shipping cost on your forms: https://www.jotform.com/help/304-How-to-Add-Shipping-Cost-to-Payment-Forms 

If you have any question, please let us know. 

Totally makes sense... Issue is when a customer orders 3 or 4 different Products that are to be shipped together. 1st product is $25 shipping then the marginal cost of each product (depending upon size) is another $10 per item.
How can we calculate this during order?
Love Jotform
Best
Henry

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Unfortunately, it is not possible to add shipping discount in this way using the inbuilt payment feature. However, you may calculate the final pricing using conditions for custom payments and send the final amount to PayPal to process the payment.

The following guide explains how to pass the calculation to the payment field.

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

Please see the demo form here, created by my colleague, for another thread about how the calculation works.

http://form.jotformpro.com/form/50771977577978?

Please feel free to clone the form to your account to make any modifications