AngularJS, datatables, and ajax call to php

I'm new to an angularjs project and one thing I've encountered is a feature that uses angular-datatables to display and populate the tables for the project. I'm trying to retrieve data using an ajax call to a php file (which uses an API call to retrieve it). Based on research, I was able to look into server side processing.

Here is the snippet from old_app.js:

.controller('BasicDatatableCtrl', function ($scope, DTOptionsBuilder, DTColumnBuilder, DTInstances, $resource) {

var vm = this;
vm.message = '';

function rowCallback(nRow, aData, iDisplayIndex, iDisplayIndexFull) {
  // Unbind first in order to avoid any duplicate handler (see https://github.com/l-lin/angular-datatables/issues/87)
  angular.element('td', nRow).unbind('click');
  angular.element('td', nRow).bind('click', function() {
    $scope.$apply(function() {
      vm.someClickHandler(aData);
    });
    angular.element('.row_selected').removeClass('row_selected');
    angular.element(nRow).addClass('row_selected');
  });
  return nRow;
}

vm.dtOptions = DTOptionsBuilder.newOptions()

        .withOption('ajax', {
        url: './ajax/ajax_data.php',
        type: 'POST'
    })
    .withDataProp('')
    .withOption('processing', true)
    .withOption('serverSide', true)
    .withPaginationType('full_numbers');   

vm.dtColumns = [
  DTColumnBuilder.newColumn('id').withTitle('ID'),
];

DTInstances.getLast().then(function (dtInstance) {
        vm.dtInstance = dtInstance;
    });

    vm.reload = function(event, loadedDT) {
        vm.dtInstance.reloadData();
    };

function someClickHandler(info) {
  vm.message = info.verticals + ' - ' + info.SoldPer;
}

vm.someClickHandler = someClickHandler;

})

Here are the contents of ajax_data.php:

<?php
echo "[{
"id": 860,
"firstName": "Superman",
"lastName": "Yoda"
}, {
"id": 382,
"firstName": "Someone First Name",
"lastName": "Bar"
}]";
?>

The problem is I'm not getting any results at all. I've tried the solution to this link but I was not able to get it to work: Angular-DataTables custom filter