Dynamic Loader in Kendo Grid?

Question

I am trying to add combo box loader in kendo grid filter using this link https://www.telerik.com/kendo-angular-ui/components/dropdowns/combobox/filtering/#toc-server-side-filtering I am getting invalid template error.My use case is I need to have multi combobox in filter,so that user can select multiple entries using api call. I am quite new to this,any help how we can achieve this.

Sample Code:

 $(function(){
        $("#grid").kendoGrid({
          dataSource: products,
          filterable:    true,
          height: 400,
          columns: [
            {field: "CategoryName",
          filterable: {
                multi:true,
                 itemTemplate: function(e) {
                    return '<my-app> <span class="k-icon k-i-loading" style="color: #ff6358"></span> </my-app>'
                }
            }
            }]        
            });
        });