Not only “have you created the UI”, but is it actually added to the view port? Read the description of the boolean on the node.
Anyway, consider creating a variable that directly references the things you want to access rather than finding them.
Another thought is, does that graph actually work? I mean, the first pin of the sequence leads to the output, so I don’t think sequence 2 and 3 ever executes? Try moving the output node to after “update ammo”