I think what you need to do is simply the following
</script> $(document).ready(function () { $('#example').dataTable({ "ajax": "/Home/Index", "columns": [ { "data": "FirstName" }, { "data": "LastName" }, { "data": "Username" }, { "data": "Password" }, ] }); }); </script>
No need for the processing and serverside and they are used when you have large data and would like to have paging and sorting done on the server side which is not the case in your code

I think what you need to do is simply the following
</script> $(document).ready(function () { $('#example').dataTable({ "ajax": "/Home/Index", "columns": [ { "data": "FirstName" }, { "data": "LastName" }, { "data": "Username" }, { "data": "Password" }, ] }); }); </script>
No need for the processing and serverside and they are used when you have large data and would like to have paging and sorting done on the server side which is not the case in your code