unity unable to convert to dex format, need help fast.

Help, when ever i build my android app, which includes the android sdk only, not android studio, and jdk 8, and also a plugin for unity ads, unity states that it was unable to convert classes into dex format. i think it has something to do with the unity ads plugin, but i dont know what, and its my first time creating an android app.
stderr[ Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/ads/BuildConfig; Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/ads/IUnityAdsListener; Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/ads/UnityAds; Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/ads/UnityAds$1; Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/ads/UnityAds$2; Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/ads/UnityAds$FinishState; Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/ads/UnityAds$PlacementState; Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/ads/UnityAds$UnityAdsError; Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/ads/adunit/AdUnitActivity;