We're getting a mysterious checkout failure (see attached screenshot) on items that don't ship (ie, PDFs, shipping service upgrades, etc.) It says at the top "1 required piece of information is missing" but then nothing on the form is highlighted in red. Obviously, this is a painful experience for the customer with no clear way to proceed.
Also, here is the add to cart link that initiated this checkout procedure: https://leafcutter.foxycart.com/cart?category=upgrade&name=FedExMexico&price=37
Our "upgrade" category is for non-shippable products. Can you identify the problem and help us fix? Thanks.