At the firm I work at, one of my "10% time" projects was to build out a "warnings" field in the API response. There are often times that you want to say "this is not inherently wrong, but likely represents wrong assumptions upstream" or "you're asking for something that's obsolete and is now being silently ignored".
For example, if someone passes a currency field with the wrong number of decimal places. You might actually want to say your product costs $1.62346, but it's more likely you're not sanitizing your data and relying on non-guaranteed rounding behaviour to make it right.
The problem we have is that the most of the API fields are opt-in-- the people who could most use the warnings are unlikely to go in and activate them.
To be honest I think the robustness principle isn’t very well supported. We shouldn’t be this accommodating in what we accept. We’re very likely harming users by ignoring errors.
