by Juan Leyva.
Please,
follow again this instructions step by step (double check that everything is well configured):
https://docs.moodle.org/28/en/Moodle_Mobile_additional_features#Installation
It seems that you haven't enable correctly the plugin so the app doesn't detect it, maybe you should also uninstall the app and re-install it again (to delete any cached data)
Cheers, Juan