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JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
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I was a able to see the issue you're describing, the coupon looks valid but it doesn't change the price of the first 3 items you included in the coupon.
So I cloned your form and recreated that same coupon, and it worked. Here's how it went from my perspective:
I would recommend you do the same - Just delete the coupon then re-add it on your Paypal Payment field to see if that will help.
If the issue persists, just get back to us so we can have another look.