Acess denied in oAuth2

I am trying to send string data from Android app to ErpNext, I am impelmenting oauth2 by refering following link
now i am able to get authorization code(as reflected in ERPNext as well as i can see in logcat in android studio). But i am not able to get access token , it gives following output

MY_TAG: OAuth2AccessToken{access_token={“error”:“access_denied”}, token_type=null, expires_in=null, refresh_token=null, scope=null}
2019-01-24 13:12:09.355 15509-15509/? I/Timeline: Timeline: Activity_launch_request time:51550477 intent:Intent { act=android.intent.action.VIEW cat=[android.intent.category.BROWSABLE] dat=oauth2://frappeclient?code=AWus33XMZtJoiuF1LLCDr8ltgmgdgm flg=0x14000000 (has extras) }