Issue in using Set Integer (by ref) in a macro

Hello, I am trying to set the value of an integer by reference in a macro created in my blueprint script. I was using one of the maze generating tutorials and the function throws a failed to resolve term Value passed into Target error. I am not sure why it cannot deduce the type of Value. The original tutorial was made in UE 4.6, so could it be due to updates made in UE 4.16?
I have attached a screenshot of my blueprint

This usually happens when the macro is called and the referenced variable is not valid / not plugged in outside the macro itself. Make sure all ‘plugs’ are connected. Another alternative would be, as mentioned in other forums, use the IncrementInt (++)

I’m not sure i understand what “called and the referenced variable is not valid / not plugged in outside the macro itself. Make sure all ‘plugs’ are connected” means. I can’t think of a way in which it makes sense. Perhaps an example? Thanks in advance.