Hello I want a datatable with checkboxes. For the data in the table I'm using a ajax call. Can anyone help me because the table is not showing the checkboxes. All the rest of the data is showing perfect.

  $(document).ready(function () {
    $("#donaties").DataTable({
      ajax: {
        url: "fitness_2020.json",
        dataSrc: "",
      },
      columns: [
        { data: "Maanden" },
        { data: "Benchen" },
        { data: "Squatten" },
        { data: "Deadliften" },
      ],
      pageLength: 25,
      aaSorting: [],
    columnDefs: [ {
        orderable: false,
        className: 'select-checkbox',
        targets:   0
    } ],
    select: {
        style:    'os',
        selector: 'td:first-child'
    },
    order: [[ 1, 'asc' ]]
    });
    var table = $("#donaties").DataTable();
  });