function already defined

You would want to use a blueprintnativeevent then.

Here is rama’s wiki on the differences and uses of those two types

https://wiki.unrealengine.com/Blueprints,_Empower_Your_Entire_Team_With_BlueprintNativeEvents

https://wiki.unrealengine.com/Blueprints,_Empower_Your_Entire_Team_With_BlueprintImplementableEvent