Below is my table:

<table class="genericTable" id="docTable" style="width:100%">
            <thead>
              <tr class="tableHeader">
                <th>Workplace</th>
                <th>Group</th>
                <th>Step</th>
                <th>Active</th>
              </tr>
              <tr class="searchRow tableHeader">
                <th></th>
                <th></th>
                <th></th>
                <th></th>
              </tr>
            </thead>
          </table>

Here is where I populate it:

var docDT;
/**
 * Generates the Main Table
 */
function getChecklist() {
  //Initialize DataTable
  docDT= $('#docTable').DataTable( {
    display: 'envelope',
    ajax: {
      'type': 'POST',
      'url': './ajax/getData.ajax.php',
      'data': {
        'getChecklist': 1,
      }
    },
    table: ('#docTable'),
    orderCellsTop: true,
    searching: true,
    paging: true,
    bInfo: true,
    iDisplayLength: 50,
    scrollX: true,
    dom:
      "<'row'<'col-12 col-sm-6 col-md-4 col-lg-3'l><'col-md-4 col-lg-6 d-none d-md-block'><'col-12 col-sm-6 col-md-4 col-lg-3'f>>" +
      "<'row'<'col-sm-12'tr>>" +
      "<'row'<'col-sm-5'i><'col-sm-7'p>>",
      columnd: [
        { data: null, render: function ( data, type, row) {
          return "<a class=\"default-link\" onClick=\"viewDocEntry(" + data.id + ")\">" + data.area + " (Rev:" + data.rev + ")";
        } 
        },
        { data: "grouping" },
        { data: "step" },
        { data: "active" },
      ],
    fixedColumns: {
      leftColumns: 1
    },
    initComplete: function () {
      
      //This Draws The Option For The Table For Static Row
      this.api().columns([0]).every( function () {
        var column = this;
        
        var select = $('<input type="text" class="fixed_col" placeholder="Search" />')
          .appendTo($(column.header()).parent().parent().children('tr').eq(1).children('th').eq(0).empty() )
          .on('keyup change clear', function () {
            var val = $.fn.dataTable.util.escapeRegex(
              $(this).val()
            );
            
            column
              .search( this.value )
              .draw();
          });
      });
      this.api().columns([]).every( function (index) {
        var column = this;
        var select = $('<input style="width:80%;" type="text" placeholder="Search" />')
          .appendTo($(column.header()).parent().parent().children('tr').eq(1).children('th').eq(index).empty() )
          .on( 'keyup change clear', function () {
            var val = $.fn.dataTable.util.escapeRegex(
              $(this).val()
            );
            
            column
              .search( this.value )
              .draw();
          });
      });
    }
  });
  
  docDT.buttons().container()
    .appendTo( '#docTable_wrapper .col-md-6:eq(0)' );
    
  $( docDT.table().container() ).on( 'keyup change clear', '.fixed_col', function () {
    docDT
      .column( $(this).data('index') )
      .search( this.value )
      .draw();
  });
  
  //Wait Half A Second For Tables To Finish And Align Columns
  setTimeout(fixColumns, 500, docDT);
}

Where is the error coming from and what could I do to fix it?