How do I redirect on flag save programmatically?
This can be done in hook_entity_presave().
function MYMODULE_flagging_presave(FlaggingInterface $flagging) {
  switch ($flagging-&gt;getFlagId()) {
    case 'FLAGTYPE':
      $redirect_url = Url::fromRoute('view.VIEW_MACHINE_NAME.VIEW_DISPLAY_ID')-&gt;toString();
      $response = new RedirectResponse($redirect_url);
      $response-&gt;send();
     break;
   }
 }