Personally I found no situations where oversimplified indication of failure is fine in such contexts. If service is down users should know it is down and it is

Personally I found no situations where oversimplified indication of failure is fine in such contexts. If service is down users should know it is down and it is not a failure of their device or network connection. It is normal to skip specifics that developer need for debugging but simply indicating a failure will just annoy users because they won't know what they could do. And contacting support each and every time is tiring and counterproductive for everyone involved. It can be error code or somewhat generalized textual description but it gives users feeling of control which most people like to have.