Why: A pin expected an actor of type '{expected}' (or subclass) but you connected a '{actor}' which doesn't inherit from it.

Fix: Either: (a) change your '{actor}' to inherit from '{expected}' by reparenting it (File → Reparent Blueprint), or (b) use a Cast To node to verify the type at runtime, or (c) plug in a different actor that IS a subclass of '{expected}'.