How do I properly use an interface?

I have been trying every which way to get this interface to work with no luck and I have no idea what the problem is.
I was looking at the UE4 documentation, and I implement the interface in each of my blueprints, but it wont let me make an event so I can send variables!

In this example for testing purposes, I have build a fog gate similar to the ones in the dark souls games. The default state of this gate is “areablocker”, meaning that it blocks navigation to the area and cannot be interacted with. By interacting with the NPC “Brain” in front of the gate, he would tell you there is a monster ahead, and then “Brain” would send the value “BossGate” in variable “GateType” over to the gate via interface, which would make the gate to be interacted with.

Can anyone explain/post a BP showing how this should be set up in “Brain”, “FogGate”, and the interfaceBP?

Solution: I had inputs and outputs set up on the interface. Looks like it only works if you only have Inputs (in the target bp they are available as output pins appartently)

It actually will work with outputs, you just have to use a function for the interface when outputs are present (because events can’t return anything).