[kiitos]

> I just find it super strange that people want to mirror their app logic + error response codes to some protocol like HTTP – ridiculous :)

Why is this ridiculous?

HTTP is the default protocol for network services, so it seems to me that it is perfectly sensible to design your API to be compatible with HTTP semantics.

> Why not go even lower as TCP and use some of that spec for our client <> server API conn. Many people will laugh, but if you think about it, where is the difference?

Because HTTP is the only protocol that can reliably transit arbitrary networks (middle-boxes, NAT, etc.) in practice.