Yeah exactly the thing I recommended 
But I wanted to explain all dependencies one class should have.
When I first used Unreal there were many Errors and I didn’t know why, until I realized that the Naming Conventions etc. where essentially. (F before struct name, U before Object and/or Components A before Actor)
Also other things like .generated.h and so on are things you have to know when using Unreal Engine, because the Compiler is not a help, when trying to find the error.
So I tried to show him all the things he has to be careful at.
But fortunately the problem is solved now 
Good luck
Greetings