I am very new to this UE4 but I have been working a lot with the HUD class. I believe your Function of Call Play Matinée needs to target the set variable of the associated widget. I created a HUD that looked very similar to yours (without the Matinée). I had to target the function to where the widgets variable was set. I am very new to this and might be wrong please feel free to correct me, I am a total newb.