Method not allowed in Laravel. Why in this case?

I would like to know why I have a "Not Allowed" method in this case. I'm trying to set a value to NULL (I have an hasClone column) when I delete an entry that I duplicated.

My controller :

public function destroyChanges($id)
  {
    $activity = Activity::findOrFail($id);
    $activity->delete();

    return redirect()->to('/admin/activity/setCloneNull/' . $activity->parent_id);
  }

public function setCloneNull($id, Activity $activity)
{
  $activity = $activity->where('id', '=', $id)->first();
  $activity->hasClone = NULL;
  $activity->save();
  return redirect(url('/admin/activity/'));
}

Routes :

  Route::delete('activity/destroyChanges/{id}', ['as' => 'cancel.activity', 'uses' => 'ActivityCrudController@destroyChanges']);
  Route::post('activity/setCloneNull/{id}', ['as' => 'setCloneNull.activity', 'uses' => 'ActivityCrudController@setCloneNull']);

How to make it work? thank you !

via Chebli Mohamed