How do you know what's gone wrong when your API request fails?

Your generic HTTP client could provide fine-grained details for any error automatically, your client error handling could easily & reliably differentiate specific errors you care about, and you could handle common errors across many different APIs with one set of shared logic. APIs could more safely evolve error responses, knowing that error type identifiers ensure clients will still consistently recognize errors even if explanation messages change. Custom API clients could check error types to handle specific cases easily, all in a standard way that could work for every API you use, rather than requiring a from-scratch API wrapper and epic boss fight against the API documentation every.