No way the 'postmessage' in the place of redirectUrl is worked for me. I was stuck in this portion for 2 days. I was trying different methods/approch to figure out why I'm getting "redirect_url_mismath" error. I was basically giving my google console's "Authorized redirect URIs" after clientId and secrets. Anyway why the postmessage works in there and not the actual redirectUrl. I don't get it, Can someone please tell me why its happening?