Hud_Blueprint to Level Blueprint

I want to have a slider in the Hud which controls the rotation of a cube in the level

In the Hud_Blueprint i have the slider i made in a Widget_Blueprint. Works perfect, printline values from 0 to 1 I tried to use a Interface_Blueprint, like in the following link without success. Pass Variable from HUD Blueprint to Level Blueprint - UE4 AnswerHub

my Blueprints: Dropbox - Error

Seems like i have no connection between the Blueprints.

The function works just in the Hud_Blueprint.

also the Interface Blueprint is a bit confusing for me, according to the document i need to implement the function through a event with the name of the function ?
But only for functions without an output i get associated event nodes.