I don't get why "Failed to find variable property"

Hey!
I have a little problem and I can’t find the right answer to this in the internet.
I’m a beginner and I don’t get why this boolean can’t find the property.
What should I must do? (I hope it is not so complicated)

You need something to call the Cube_Blueprint such as event begin play

Thank you! Maybe (would be so nice) you could help me again… When I shoot on a box, the bool get true. But I can’t get this bool in my user widget -event graph because the object is not defined, but I have no idea, what kind of object I have to link up… I tried everything.