Cannot add heel sound to armor addon entry?

[Random987654]

Hey,

 

I want to add heel sound (Heels Sound 1.6 SSE - AE) to my boots, I think I know how and where to do it but I always get this error and the drop down won't let me select the heel sound of the mod. Anyone can help how to fix this? 

 

Edit: I learned that I need to set the heel sound esp as master, solved, can be deleted or left open if anyone else might benefit from this

 

Edited March 31 by Random987654
Solved