There’s no dedicated documentation for the matHELICS API at this time as the API is virtually identical to the other higher level languages such as Python and Julia. Of particular note, as in those two languages, matHELICS supports the use of complex as a native data type. So
helicsInputGetComplex() returns a complex value not a list of two floats, one for the real and one for the imaginary.
There is also inline documentation in the source code files that may be helpful in providing insight.