Highcharts pie charts served from AJAX call

I am trying different ways of rendering json data from mysql/php to Highcharts. So far I've been successful rendering bar charts using this approach but for some reason, I have not been able to render data in a pie chart.

One js file handles the AJAX call:

$(function  () {

var select_program = program_type_php;
var select_year = '2016';

console.log ('pie_chart'+program_type_php);

 $.ajax({
url: 'model/job_group_pie_chart.php',

data: {user: 2, select_program:select_program, select_year:select_year},
type: 'GET',
async: true,
dataType: "json",

success: function (year_2016) {
   pie_chart_2016(year_2016);
    console.log('data 2016 job groups'+year_2016);




}

});

Upon success, I call a function in another js file (in this example, 'pie_chart_2016' and pass it the data object.

Here's the other js file responsible for rendering the data into a Highchart:

function pie_chart_2016 (year_2016) {

console.log('year_2016'+year_2016);
$('#pie-chart1').highcharts({
    chart: {
        plotBackgroundColor: null,
        plotBorderWidth: null,
        plotShadow: false,
        type: 'pie'
    },

    title: {
        text: ''
    },
    tooltip: {
        pointFormat: '{series.name}: {point.percentage:.1f}%'
    },
    plotOptions: {
        pie: {
            allowPointSelect: true,
            cursor: 'pointer',

            dataLabels: {
                enabled: true,
        format: '{point.name}: {point.percentage:.1f} %',
                style: {
                    color: (Highcharts.theme && Highcharts.theme.contrastTextColor) || 'black'
                }   

                },

                showInLegend: true


            },
        series: year_2016

        }
});

};

I have checked, and I do get valid json from my php file:

 [{name:"Group1",y:829},{name:"Group2",y:9247},{name:"Group3",y:71}]

These are raw counts (829, 9247, 71) but when I was able to get a pie chart to render by inputting values manually, Highcharts calculated the percentages for me - nice!

I've also set up enough console.logs to know that my functions are being called, and that my data object is being processed.

Still, all I get is a blank panel, and 'highcharts.com' in the lower left hand corner, so the html is working too.

The approach I'm using works really well with bar charts, so I am stumped!

Thanks for any help you can provide.