> Given that this is a totally brand-new concern, I didn't think so.

What about when the amount on a debit is higher that what Balanced, the network, or the bank support?

> I'm not sure how it would be ambiguous. It's a unique value.

Then why specify that it's a 409 vs. 400 vs. 402? They're unique values.

You're relying on the engineer/implementer to make a decision for the design. What if they copy/paste from another error and include the wrong error message? What is supposed to check that if the scenarios don't?