Export datatable to Excel

I have been using this code for awhile to allow users to export a datatable to Excel. However the export buttons no longer appear (the website is for internal-use only and I cannot provide a link to it). I using DataTables 1.10.18:

"buttons": [
    {
        extend: 'excelHtml5',
        text: '<i class="fa fa-files-o">Click here to export two years of data to Excel</i>',
        titleAttr: 'Export'
    }
        ]