FPoly::OnPoly()

Does anyone have an example of OnPoly() working? I made an FPoly object and i can get OnPlane() to work but I have trouble with OnPoly.
The output:
1>MyPawn.cpp.obj : error LNK2019: unresolved external symbol “public: bool __cdecl FPoly::OnPoly(struct FVector)” (?OnPoly@FPoly@@QEAA_NUFVector@@@Z) referenced in function “public: void __cdecl AMyPawn::Kounao(void)” (?Kounao@AMyPawn@@QEAAXXZ)

btw, I`m a newbie. I managed to make it work by copying the declaration of OnPoly inside a function of my Script.(Indirect solution) I guess it was a linker problem but not sure why…

Ran into the same issue and fixed it by declaring OnPoly as ENGINE_API in the engine.