Error after activating ads from services

So as soon as the ads are turned on from the services menu, I get this error when trying to build the apk: CommandInvokationFailure: Unable to convert classes into dex format. C:\Program Files\Java\jdk1.8.0_181\bin\java.exe -Xmx2048M -Dcom.android.sdkmanager.toolsdir="C:\Users\danny\AppData\Local\Android\Sdk\tools" -Dfile.encoding=UTF8 -jar "C:\Program Files\Unity\Editor\Data\PlaybackEngines\AndroidPlayer/Tools\sdktools.jar" -

stderr[ Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/ads/BuildConfig; Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/ads/UnityAds$UnityAdsError; Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/ads/mediation/IUnityAdsExtendedListener; Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/ads/metadata/InAppPurchaseMetaData; Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/ads/metadata/MediationMetaData;

UNEXPECTED TOP-LEVEL EXCEPTION: java.lang.RuntimeException: Translation has been interrupted at com.android.dx.command.dexer.Main.processAllFiles(Main.java:614) at com.android.dx.command.dexer.Main.runMonoDex(Main.java:310) at com.android.dx.command.dexer.Main.runDx(Main.java:288) at com.android.dx.command.dexer.Main.main(Main.java:244) at com.android.dx.command.Main.main(Main.java:95) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at SDKMain.main(SDKMain.java:130) Caused by: java.lang.InterruptedException: Too many errors at com.android.dx.command.dexer.Main.processAllFiles(Main.java:606) ... 9 more ]

but when ads are turned off it builds fine? ads don't work obviously...

any help would be appreciated!