Before I spend the time to put out a PR on this, I want to get some initial feedback. I think there are many kinds of PaymentItems that could be interesting/impactful to the payment app. I still like calling out the total as a separate item, but I would like to propose we go a step further and give all PaymentItems a type.

The PaymentItemType enum would provide a way to assign specific meaning/semantics for common use cases, e.g. taxes, discounts, etc. We would control this enum and make additions to it as needed. The enum would have a fallback value that means the PaymentItem is purely for display and has no significant meaning beyond the merchant's purposes.

What do you think? With moderate approval I will code it up.