Sending and getting an Array using fnServerParams

I am having problems sending and getting data from an array using fnServerParams. Can some one please help?
Thanks my javascript code

function generateDataTable(subject, checkboxes) {

    
    var oTable = $('#datatable1').dataTable({
        "bProcessing": true,
        "bServerSide": true,
        "sAjaxSource": base_url() + '/' + 'ccreateexam/getQuestions',
        "fnServerParams": function(aoData) {
            aoData.push({"name": "subject", "value": subject});
            aoData.push({"name": "checkboxes[]", "value": checkboxes});
           
        },
        "bJQueryUI": true,
        "sPaginationType": "full_numbers",
        "iDisplayStart ": 20,
        "oLanguage": {
            //"sProcessing": "<img src='<?php echo base_url(); ?>assets/images/ajax-loader_dark.gif'>"
        },
        "fnInitComplete": function() {
            oTable.fnAdjustColumnSizing();
        },
        'fnServerData': function(sSource, aoData, fnCallback)
        {
           // alert(sSource);
            $.ajax
                    ({
                        'dataType': 'json',
                        'type': 'POST',
                        'url': sSource,
                        'data': aoData,
                        'success': fnCallback
                    });
        }
    });
}

And in my controller

public function getQuestions() {
        
        $subject = $this->input->post('subject');

        $checkboxes = $this->input->post('checkboxes');
       
        echo $this->mcreateexam->getQuestionsForSubjectLessons2($subject, $checkboxes);

    }

Thanks