this.questionclick not working in mobile view

Hello. 
Apologies if i have missed this answer elsewhere. 
I have a slider, and I want to dynamically update the difference between player 1 and player 2's income as a function of the quantity player 1 gives to player 2 (this quantity is chosen by using the slider).
The below runs fine on a desktop, and works fine in the 'mobile view' when I preview the survey on a desktop. However it does not update when I view the preview on a mobile, nor when I publish and view on a mobile.
Any tips re. getting this to work on a mobile would be much appreciated :)

Qualtrics.SurveyEngine.addOnload(function() {
var give=0;
var give2 = give*2;
var final_difference = 0;
var inc="${e://Field/income_final}";
var partner_inc = "${lm://Field/1}";

this.questionclick = function(event,element){
 give = this.getChoiceValue(1);
give2 = give*2;
final_difference = "${e://Field/income_final}" - give - "${lm://Field/1}" - give2 ;
inc = "${e://Field/income_final}" - give;
partner_inc = "${lm://Field/1}" + give2
  endupdate();
document.getElementById("final_difference").innerHTML=final_difference;
document.getElementById("give2").innerHTML=give2;
 document.getElementById("give").innerHTML=give;
document.getElementById("inc").innerHTML=inc;
document.getElementById("partner_inc").innerHTML=partner_inc;
}

function endupdate() {
give = give;
give2 = give*2;
final_difference = final_difference;
inc = inc;
partner_inc = partner_inc;
}
});