> The server may respond in some way, yes, but we don't make any guarantees to our customers that it does. It could do absolutely anything. It's true that that exists but that doesn't mean it's useful in any way.

What are API specification supposed to do if not specify the behavior of the API?

> Well, I doubt that anyone has that big of a limit, so it would probably get declined for being over the limit. Which is distinct from 'a card network doesn't support this kind of transaction,' at least in my mind.

No network supports transactions of that size. Amex has the highest limit at $10mm. Balanced has a default card limit of $15k, so it wouldn't even make it past that even if the cardholder had a credit limit greater than that. That's what I mean by Balanced vs. bank vs. network limits.
1. Balanced limit => marketplace should contact Balanced
2. Bank limit => cardholder should contact bank
3. Network limit => can't do anything about it other than maybe split up the transaction

> Their application's tests? If someone writes bad client code, I can't debug it for them. The error message they display to their users is completely out of the scope of our API.

To clarify, what happens when a Balanced engineer returns a message in an error that doesn't make sense but is in the schema?