How are you getting the reference to Barracks in the first image?
It looks to me like you have set up a variable for it of the type Barracks BP. But you still need to Set it with the correct reference.
You could add something like this to Beginplay (or as the first thing you do in this event):
Get all actors of class (Barracks BP) → GET entry 0 from the resulting array (assuming there is only 1 Barracks BP in your level) → SET this as your Barracks BP.
After that you will be able to talk to the correct Barracks BP and the dispatcher will probably work.