Error editing an entity with a unique Laravel field

I have an entity activities with the following Form Request as indicated in the documentation

public function rules()
{
    return [
        'name' => "required|max:200|unique:activities,name,". $this->activity_id
    ];
}

When editing, send the data by axios:

    $("#frmEditActivity").submit(function (e) {
                e.preventDefault();

                axios.patch("/admin/actividades/" + $("#frmEditActivity #activity_id").val(), $(this).serialize())
                    .then(function (response) {
                        self.loadTable();
                        toastr.success(response.data);
                        $("#mdlEdit").modal('hide');
                    })
                    .catch(function (error) {
                        error.response.status == 422 ? toastr.error(error.response.data.errors.name) : "Ocurrió un error. Intentelo de nuevo!";
                    });
            });

and when sending the data I receive the following error:

  

SQLSTATE [23000]: Integrity constraint violation: 1062 Duplicate entry   'xxx' for key 'activities_name_unique

The route is:

 Route::resource('actividades', 'ActivityController', [
    'except' => 'create', 'edit', 'show',
    'names' => 'activities'
]);

The driver is:

   public function update(ActivityRequest $request, ActivityModel $activity)
    {
        if ($request->ajax()) {

            if ($this->activityRepo->edit($request->all(), $activity)) {
                return response()->json('Actividad editada correctamente.');
            }

            return response()->json('Ocurrió un error. Por favor inténtelo nuevamente!');
        }

        return redirect(route('admin.activities.index'));
    }