M
I noticed that in online documentation (APIs -> Client APIs -> Remote object system -> Callback as function arguments) might have some outdated information.
I was able to figure out, that app creates api function with signature sum: (a: int, b: int, success: (int) -> void, error: (int) -> void) -> void
instead of sum: (callback: (int) -> void, a: int, b: int) -> void
So in that case example would be
POST /myobject/functions/sum HTTP/1.1
Host: localhost:2015
Client-ID: R4Nd0M
Source-ID: 30
Content-Type: application/json
Content-Length: 15
[1,2,314,315]