Add “PhysicsCore” to your dependency module in your build.cs file.
If that doesn’t work try to include #include “Chaos/ChaosEngineInterface.h” in SWeapon.
LNK (Linker) errors are caused by some class or other not knowing what something else is at compile time. Basically, the compiler cannot compile your SWeapon because it doesn’t know what an EPhysicalSurface is.