Retrieve a hidden value in C# that was set in javascript

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C#

I have a screen that gets displayed and depending on some answers, I dynamically build a radio button list and calculate its values in javascript. The selected value I save into a hidden field. In C# the value of the hidden field is always "".

This is sort of what I have:
MY HTML - shows 3 radio button options whose values are derived at run time in javascript based on answers provided on the screen once page has loaded

<div class="testSection">
<asp:HiddenField ID="hidAnswer" runat="server" />
<asp:HiddenField ID="hidMin" runat="server" />
<asp:HiddenField ID="hidMax" runat="server" />
<table class="testTable" >
<tbody>
<tr>
<td style="padding-left: 18px">
<asp:Label ID="lblPrompt" runat="server"></asp:Label>
</td>
</tr>
<tr>
<td id="rbtNoLapse">
<div id="dvnTest1" title="rbTest1" >
<input id="rbtNo" type="radio" name="Lapse" />
<label id="LblNo" for="rbtNo" ></label>
</div>
<div id="dvMin" title="rbTest1" >
<input id="rbtMin" type="radio" name="Lapse" />
<label id="LblMin" for="rbtMin" ></label>
</div>
<div id="dvMax" title="rbTest1" >
<input id="rbtMax" type="radio" name="Lapse" />
<label id="LblMax" for="rbtMax" ></label>
</div>
</td>
</tr>
</tbody>
</table>
</div>

In javascript while validating the the selection I get the selected item. The alert is showing the correctly selected item in the hidden field hidAnswer.

var list = document.getElementById("rbtNoLapse");
var inputs = list.getElementsByTagName("input");
var selected;


for (var i = 0; i < inputs.length; i++)
{
if (inputs[i].checked)
{
selected = inputs[i];
break;
}
}
if (selected)
{
hidAnswer = selected.value;
}
alert( hidAnswer);




in C#, getting the values from the form, for both hidden fields the value = "" - I dont understand why they do not have the same values as is showing in the alert in javascript.

if (hidMin.Value != "0")
{
if (hidAnswer.Value == "01")
{
do something
}

}


I cannot find a simialr scenario that I can refer to - I have searched all over.
Any help is appreciated.

What I have tried:

I have searched all over for a similar scenario but could not find one exactly like mine. I have tried loads of suggestions but nothing works. Im obviously doing something wrong, have bad syntax or trying to do something thats just not possible ! Any help is appreciated.