I'm not the original poster, but I also had the same issue. I'm not in an incognito window nor do I have any special privacy mode (I'm using Chrome on OSX).

Error 400: redirect_uri_mismatch The JavaScript origin in the request, https://www.getpingpong.com, does not match the ones authorized for the OAuth client. Visit https://console.developers.google.com/apis/credentials/oauth... to update the authorized JavaScript origins.