Function" particle-function: in Rule engine

Hi, I'm new at Node-Red and also at Rule engine.
I got a particle function implemented on Photon device code.
I verified the correct function operation using particle console.
Apparently the issue I have is setting the function "particle-function on Rule engine.
Please see attached pic

A slider send a numeric value through the function "particle-function" called sliderhp.
and at the debug pane one can see the slider value and msg.payload , where payload property is =1.
I understand that this one is the return of the function called on particle device.

This is the Phoron device function called:

int sliderhp (String valor ) {

 sliderHPvalue=atoi (valor);
 Serial1.println (sliderHPvalue );
 return 1;  


If I set some value on the dashboard's slider, on the debug pane you got payload=1.
But on the terminal, I got printed out "0" trough the Serial1.println (sliderHPvalue );.

My point is that in the node properties for that function "particle-function", I don't know
what should be the correct function argument . Please see attached pic.

It should be the slider payload but I do not succeed in the correct format it should have.
Thank you for some help.