Hi Chris,
Maybe you already figured this out, but you need to set the redirect uri in ArcGIS Online as follows for Android devices...
urn:ietf:wg:oauth:2.0:oob
Should work then.
Hi Chris,
Aaron is true, if you want to use your organization account to license your app in Standard level, you must specify redirect url to ArcGIS Online using : urn:ietf:wg:oauth:2.0:oob (as explained by Aaron). I already successfully using it a few months ago.