in Dynamics 365 CRM form there's a checkbox field named opu_paid, if its unchecked, im supposed to disable all fields in the form in javascript. so far im stuck in my code on how to get the value from this checkbox field (wether its true or false) so i can use "setDisabled" method

How do i get the the checkbox field value ?

var formContext = Context.getFormContext();
var paidCheckbox = formContext.getAttribute("opu_paid").getValue() // this is not working 

if(!paidCheckbox)
{
    formContext.getControl("firstname").setDisabled(true);
    formContext.getControl("lastname").setDisabled(true);
}
else
{
    formContext.getControl("firstname").setDisabled(false);
    formContext.getControl("lastname").setDisabled(false);
}